What is heat?

[spin-1/2-nuclei]

Before reading this post please see the definition of terms. This is how these terms are being used in the context of this post.

 

1. thermal energy - I am using the definition of thermal energy commonly employed when speaking about the temperature of a system that results from molecular movement. i.e. thermal energy = translational kinetic energy/random kinetic energy

2. Kinetic energy - the energy arising from molecular motion

3. average translational kinetic energy (sometimes interchanged with kinetic energy for brevity (see context of sentence to decide)) - the kinetic energy of the higher energy system that is being transferred - (via molecular collisions) - to another system of lower energy. Synonomous with thermal energy.

4. Random kinetic energy - see average translational kinetic energy.

5. Heat - the transfer of energy via translational kinetic energy - measured/described by temperature

6. Temperature = directly proportional to thermal energy/translational kinetic energy - the intensity of the energy NOT the amount.

 

Two samples of a substance, but one is twice the amount of the other. They have the same temperature. They do not have the same amount of thermal energy. This is an important point that was missing from the description.

 

Temperature is directly proportional to the average kinetic energy. Thus, if you have two samples, and they are at the same temperature their average kinetic (random/translation) energy is the same.

 

You are confusing the heat capacity (amount of heat required to change the temperature of the entire sample by 1 unit)/specific heat (the amount of energy required to change the temperature by 1 unit of one kg of the substance) -

 

these depend on the amount of the substance as well as it's identity, etc, etc -

 

with "thermal energy"... Which IS kinetic (translational/random) energy, because they (thermal/kinetic energy) refer to the intensity (i.e. the temperature) of the heat not the amount of it.

 

That is to say, there is a difference between the amount of heat transfered/held (heat capacity/specific heat) I can transfer from one object to another and the intensity (kinetic/thermal energy) of the heat I am transferring. That is to say two suns in the universe might both be red giants (i.e. they have the same intensity (thermal/kinetic energy)) but if one can fit inside the other 20 times, then they will not have the same amount of heat (heat capacity/specific heat)..

 

Thus,

thermal energy/kinetic energy (rotational/random) in the context of heat transfer only measure the INTENSITY of the heat not the amount.

 

This doesn't mean that temperature is not related to heat capacity/specific heat, but it does not arise from them. As I said in earlier posts, that is to say that temperature can be changed via many different external forces acting on the molecular system, but these external forces (whether or not they are directly or indirectly measurable) MUST change the average kinetic energy/thermal energy - if they are going to change the temperature.

 

and as I said before,

Energy taken into the system from an external source can either go to internal energies (such as bond making/breaking, etc) or it can be converted into kinetic energy, which is the motion of the molecules, which gives rise to the temperature. That is to say things like entropy don't cause the increase in temperature, but rather cause the increase in the kinetic energy of the system, which in turn cases an increase in the temperature.

 

Two different sized pots of water will boil at the same temperature (intensity) - if all other factors in their environment are all the same - they DO NOT boil in the same length of time nor will they have the same amount of energy (specific heat/heat capacity).

 

This is because you can look at the average kinetic energy of two identical substances in identical environments (regardless of their size) as constant and mostly identical value. That is to say you won't add heat to water on monday and get a vastly different thermal energy than you will on thursday, because water molecules use energy the same way in the same environment.

 

So if we pretend that water's average kinetic energy increases per unit of Temperature is going to be 5 (imaginary energy units). Water when at 100C will be have an average kinetic energy/thermal energy/intensity whether it is 1ml or 50ml, i.e. the size of the sample does not matter.

 

(this next part is overly simplistic - i.e. I am not calculating the energies but rather making them up - but it is an accurate mathematical representation of what happens all the same)

 

So, if on average a water molecule's increase in energy (in isolation - I will deal with the environment of each individual particle next) is going to 5 per every unit of heat, then in my example above 5 molecules of water at 100 C will make the average kinetic energy (500 x 5)/5 = 500... now in the larger sample I have 20 molecules of water and they are boiling as well so I now have (20x500)/20 = 500 too.

 

Now lets take those particles out of isolation and place them in real life.

If we take note that - the kinetic energy of two identical substances in two identical environments will be the SAME - (otherwise I'm not sure what randomized kinetic energy would really do for us scientifically) - we can state that even though (due to environmental perturbations as no system is 100% uniform) the individual kinetic energies of a substance will vary within the system (that is why we say thermal energy/average kinetic energy is the average of the energies) if those particles are identical those energies will not - on average (not as the individual) vary extensively. Moreover, no matter what the size of the sample, as shown above, the intensity of the energies, remains the same.

 

thus,

5 molecules of water @ 100C

- molecule 1 = 500, molecule 2 = 500.000001, molecule 3 = 501, molecule 4 = 499.999999, molecule 5 = 500

you get

(500+500.000001+501+499.99999+500)/5 = 500,19999 = the average kinetic energy/thermal energy in my imaginary energy units for this sample..

 

 

An equal amount of two gases are at the same temperature. One of them is an ideal gas. The other is not — it's diatomic. The thermal energy of the ideal gas will be 3/2kT per particle. For the other, it will be 5/2kT. They do not have an equal amount of thermal energy. And neither the thermal energy nor the temperature is heat, which is the point of all this: there is no energy transferred, so there is no heat.

 

I never said there could be heat without energy transfer - ever.

Again, the "confusion" is because you think the word describe can be somehow more closely defined as the word is in lieu of the word measure...

 

I can't help you with that one because I intend to use the word describe as I have always used it, so why don't just agree to disagree.

 

Moreover, in this case you are using the thermal energy of two different substances - if they have different chemical structures they will not have the same intensity/thermal energy/average kinetic energy in identical environments. That doesn't mean that you can't make one gas with a different chemical structure than another gas have the same intensity/thermal energy/kinetic energy [described/measured by temperature] in different environments. The fact that no heat is transfered also has nothing to do with the kinetic/thermal energy - only the - temperature. If/when that energy is ready/able to transfer the intensity will still be the same so long as the other parameters are kept constant.

 

This is why nobody claims to know the amount of energy introduced into a system based on temperature (intensity) only.

 

hopefully this clears it up.

Cheers

Edited August 19, 2011 by spin-1/2-nuclei

[swansont]

Before reading this post please see the definition of terms. This is how these terms are being used in the context of this post.

 

1. thermal energy - I am using the definition of thermal energy commonly employed when speaking about the temperature of a system that results from molecular movement. i.e. thermal energy = translational kinetic energy/random kinetic energy

2. Kinetic energy - the energy arising from molecular motion

3. average translational kinetic energy (sometimes interchanged with kinetic energy for brevity (see context of sentence to decide)) - the kinetic energy of the higher energy system that is being transferred - (via molecular collisions) - to another system of lower energy. Synonomous with thermal energy.

4. Random kinetic energy - see average translational kinetic energy.

5. Heat - the transfer of energy via translational kinetic energy - measured/described by temperature

6. Temperature = directly proportional to thermal energy/translational kinetic energy - the intensity of the energy NOT the amount.

 

These definitions work for an ideal gas using kinetic theory, but several do not hold in general. Heat, for example, can be transferred via radiation. Also, I don't think I've ever seen "intensity" used in a thermodynamics definition of these terms.

 

 

 

Temperature is directly proportional to the average kinetic energy. Thus, if you have two samples, and they are at the same temperature their average kinetic (random/translation) energy is the same.

 

You are confusing the heat capacity (amount of heat required to change the temperature of the entire sample by 1 unit)/specific heat (the amount of energy required to change the temperature by 1 unit of one kg of the substance) -

 

I didn't use heat capacity in that example. The material is the same, so the heat capacity is the same. The difference is in the quantity of the sample. Two moles of an ideal gas has twice the energy as one mole, at the same temperature.

 

 

these depend on the amount of the substance as well as it's identity, etc, etc -

 

with "thermal energy"... Which IS kinetic (translational/random) energy, because they (thermal/kinetic energy) refer to the intensity (i.e. the temperature) of the heat not the amount of it.

 

Heat doesn't have a temperature

 

 

That is to say, there is a difference between the amount of heat transfered/held (heat capacity/specific heat) I can transfer from one object to another and the intensity (kinetic/thermal energy) of the heat I am transferring. That is to say two suns in the universe might both be red giants (i.e. they have the same intensity (thermal/kinetic energy)) but if one can fit inside the other 20 times, then they will not have the same amount of heat (heat capacity/specific heat)..

 

Heat is not "held". This is one of the issues I referred to earlier, that the naming of heat capacity gives rise to a misconception that heat is a substance or the property of a substance, and it isn't.

 

 

I never said there could be heat without energy transfer - ever.

 

Your words where you equate heat with translational kinetic energy with thermal energy (emphasis added):

Thus my statement "temperature describes - i.e. - measures - the thermal energy which is the heat - i.e. - heat = translational kinetic energy = the energy being transferred IS accurate semantically according to your own preferred source.

 

And

Temperature describes the average heat or thermal energy (this implies of a system…

A system does not have heat (more on this below)

 

Moreover, in this case you are using the thermal energy of two different substances - if they have different chemical structures they will not have the same intensity/thermal energy/average kinetic energy in identical environments. That doesn't mean that you can't make one gas with a different chemical structure than another gas have the same intensity/thermal energy/kinetic energy [described/measured by temperature] in different environments. The fact that no heat is transfered also has nothing to do with the kinetic/thermal energy - only the - temperature. If/when that energy is ready/able to transfer the intensity will still be the same so long as the other parameters are kept constant.

 

And why is using two substances a problem? Definitions need to hold in general, not for specific cases only. The bottom line is that "Temperature describes the average heat or thermal energy" is incorrect, if for no other reason than heat requires two different temperatures. It makes no sense to talk about heat for a single substance at some temperature.

 

If you disagree, here's what you can do: In physics, heat is Q. Find equations that give Q for a single substance.

[spin-1/2-nuclei]

If you disagree, here's what you can do: In physics, heat is Q. Find equations that give Q for a single substance.

 

You've misunderstood what I said. Yes I disagree with you, but it's not because I think temperature = heat or because I don't believe physics defines "heat" as Q, but rather because your position is very confused. In some cases your definitions for your terms are correct, but because your application of those definitions to the real world are flawed it is not possible to have a productive conversation. Many times you're overlooking the quantum mechanical applications of these principles, and advancements made by modern science.

 

All of my colleagues are aware of this. That is why when other people define their terms either during the body of the text or beforehand, people typically move on to understanding the content of the research in lieu of arguing about which definition of what term should have been used. A mathematical proof remains sound no matter what letter or symbol one decides to use to define the different parameters.

 

For example:

"There is some debate in the scientific community regarding exactly how the term heat should be used.[5] In current scientific usage, the language surrounding the term can be conflicting and even misleading. One study showed that several popular textbooks used language that implied several meanings of the term, that heat is the process of transferring energy, that it is the transferred energy, i.e., as if it were a substance, and that is an entity contained within a system, among other similar descriptions. The study determined it was not uncommon for a combination of these representations to appear within the same text.[6] They found the predominant use among physicists to be that if it were a substance." - http://en.wikipedia.org/wiki/Heat#Semantic_misconceptions

 

When talking about energy that has been or is being transfered my colleagues and I use "heat" and thermal energy interchangeably. When talking about energy that is contained within the system we refer to it as either kinetic energy or thermal energy. This is because from our perspective energy is never created or destroyed, thus it doesn't really matter what we call it so long as we appropriately quantify it in our system. By doing things this way, progress in research can be made. Otherwise we'd spend all of our time writing essays on the semantics of the definition of heat.

 

That is why, as you can see from the reference I've provided above, most scientist are more concerned with their research than they are with the semantics. You need a term to define the energy measured/described by the temperature and transferred between objects and systems. You've yet to provide an alternative to heat that would be functional in a research environment.

 

========================================

 

I especially take issue with your interpretation of heat and temperature.

 

"Sensible heat had a clear meaning in the writings of the early scientists who provided the foundation of thermodynamics. James Prescott Joule characterized it in 1847 as an energy that was indicated by the thermometer." - http://en.wikipedia.org/wiki/Sensible_heat

 

The above definition of "heat" corresponds exactly with mine.

 

On the other points:

I'm sorry but your interpretation of these concepts is wrong. I've already gone over why in previous posts. So, I will just address your points with quotes from scientific journal articles at this point.

 

Your statement: "Heat" cannot be stored/held & systems do not have heat. " - I'm sorry but, this is just wrong:

 

"As an alternative to storage of sensible heat in liquids or solids or as latent heat of fusion, heat storage by means of reversible chemical reactions is under investigation. By this method, a chemical is separated into two components by heating and heat absorption, following which the components are stored in separate vessels and are recombined to generate heat when it is needed. The attractiveness of this concept of heat storage is not only higher energy density, but the capability to store energy as long as desired at ambient temperature, the option of transporting the chemicals to generate heat at another location, and the high temperatures characteristic of some of the reactions which result in high efficiency when the stored heat is used to generate electricity." - http://www.sciencedirect.com/science/article/pii/0022459677901888

 

Sensible heat - is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature. (this definition came about as a direct result of semantics no doubt.) - http://en.wikipedia.org/wiki/Sensible_heat

 

More from the same source:

"The terms sensible heat and latent heat are not special forms of energy, instead they characterize the same form of energy, heat, in terms of their effect on a material or a thermodynamic system. Heat is thermal energy in the process of transfer between a system and its surroundings or between two systems with a different temperature."

 

Another source:

 

"This paper presents the results of a comparative numerical investigation on packed bed thermal models suitable for sensible and latent heat thermal storage systems." - http://www.sciencedirect.com/science/article/pii/S1359431198000817

 

======================

 

2. In regards to your comments about temperature, the sources below contradict your statements: - http://en.wikipedia.org/wiki/Temperature#Heat_capacity

 

"Temperature may be viewed as a measure of a quality of heat, as distinct from a quantity of heat.[1][2][3][4] The quality is called hotness by some writers."

 

"In the context of thermodynamics, the kinetic energy is also referred to as thermal energy. The thermal energy may be partitioned into independent components attributed to the degrees of freedom of the particles or to the modes of oscillators in a thermodynamic system. In general, the number of these degrees of freedom that are available for the equipartitioning of energy depend on the temperature, i.e. the energy region of the interactions under consideration."

 

"On the molecular level, temperature is the result of the motion of the particles that constitute the material. Moving particles carry kinetic energy. Temperature increases as this motion and the kinetic energy increase."

 

=======================

[swansont]

In each of those examples, they refer to heat as energy being transferred, not energy that is contained in a system, and all you've really shown is that people misuse the terminology. The wikipedia quote you used repeats what I've said a few times already. Also mentioned in that article: "In a thermodynamic sense, heat is never regarded as being stored within a system."

 

Heat, as its used in physics these days, is the thermodynamic equivalent to work. Work is not the same as kinetic energy, even though under some conditions the values can be equated. Work is not contained in an object. What you can do is store the energy the work represents.

 

From my perspective, I find your position that you "care about how science is presented to the world" to be inconsistent with referring to "the quantum mechanical applications of these principles, and advancements made by modern science" because someone who has little or no background in science is going to be overwhelmed by quotations of advanced concepts. When someone asks what is obviously a physics 101 question, you don't give them the physics 651 answer. Presenting science to the world includes being able to discuss it at the level the audience will understand.

[finiter]

You seem ...... I think you will have no trouble understanding these concepts ....

Thank you very much for taking so much trouble to explain in detail. I am just a layman interested in physics, 'neither a student nor a researcher' by normal standards. Incidentally, I have my own picture of the physical world, and through this post I am just trying to understand the existing standard model in unambiguous terms so that I can correct my own views wherever required.

[finiter]

Temperature is not the average heat or average thermal energy. Temperature is a measure of the average translational kinetic energy of the constituent particles. Thermal energy is more involved — you include internal energy as well.

Please explain the following situation: (I had earlier posted the same in this post, but did not get your opinion) Suppose you have two containers, one larger than the other. Let each contain the same number of atoms of the same gas, and let their average kinetic energies be the same. In that situation, will the both have the same temperature?

[swansont]

Please explain the following situation: (I had earlier posted the same in this post, but did not get your opinion) Suppose you have two containers, one larger than the other. Let each contain the same number of atoms of the same gas, and let their average kinetic energies be the same. In that situation, will the both have the same temperature?

 

Yes. The sample size and volume need not be equal to have the same temperature; all that is required is that the average KE be the same. The size of the sample will dictate the total thermal energy, and the volume will impact the total energy (PV is an energy term)

 

THis is similar to looking at some volume and then looking at a subset of that same volume.

[spin-1/2-nuclei]

Yes. The sample size and volume need not be equal to have the same temperature; all that is required is that the average KE be the same. The size of the sample will dictate the total thermal energy, and the volume will impact the total energy (PV is an energy term)

 

THis is similar to looking at some volume and then looking at a subset of that same volume.

 

This is incorrect. Temperature is directly proportional to kinetic energy/thermal energy and temperature is related to volume. See Charles' Law & adiabatic compression.

 

In this case, they cannot have the same temperature, because their volumes will not be the same. Since they cannot have the same temperature, they will not have the same kinetic energy.

 

What you're suggesting in your answer is that volume has no relationship to temperature or pressure in PV=nRT.

 

In this example the smaller container will have the smaller volume. So, the work done to compress the gas into the smaller container (because the number of gas molecules in the large container is identical to the number of gas molecules in the small container) will be transfered to the system and converted into kinetic energy, which will in turn increase the temperature. An increase in temperature results in an increase in pressure.

 

hope this helps..

Cheers

Edited August 20, 2011 by spin-1/2-nuclei

[finiter]

THis is similar to looking at some volume and then looking at a subset of that same volume.

I suspect that you have missed the point that both contains the same number of atoms. Or, is it that you actually suggest that temperatures will be the same even if the number atoms in both the containers are the same.

[swansont]

I suspect that you have missed the point that both contains the same number of atoms. Or, is it that you actually suggest that temperatures will be the same even if the number atoms in both the containers are the same.

The pressures will not be the same in the two containers. The similarity I was referring to was temperature; sorry if that wasn't clear. T is dependent only on the KE. If you change P or V, T will change.

 

This is incorrect. Temperature is directly proportional to kinetic energy/thermal energy and temperature is related to volume. See Charles' Law & adiabatic compression.

 

In this case, they cannot have the same temperature, because their volumes will not be the same. Since they cannot have the same temperature, they will not have the same kinetic energy.

 

What you're suggesting in your answer is that volume has no relationship to temperature or pressure in PV=nRT.

 

In this example the smaller container will have the smaller volume. So, the work done to compress the gas into the smaller container (because the number of gas molecules in the large container is identical to the number of gas molecules in the small container) will be transfered to the system and converted into kinetic energy, which will in turn increase the temperature. An increase in temperature results in an increase in pressure.

 

hope this helps..

Cheers

Adiabatic compression was not a condition of the example; it was not stated that the volume changed, only that it was different. You have incorrectly assumed compression/expansion to be the case. PV = nRT works just fine. The relative pressures were not specified; given the conditions you could solve for the ratio of the two. It's quite straightforward to do so.

[finiter]

In this example the smaller container will have the smaller volume. So, the work done to compress the gas into the smaller container (because the number of gas molecules in the large container is identical to the number of gas molecules in the small container) will be transfered to the system and converted into kinetic energy, which will in turn increase the temperature. An increase in temperature results in an increase in pressure.

This I think implies that some extra energy is put into it. I think that the total energy of any system can be arbitrarily fixed; there is no restriction to the amount of energy that can be possessed (of course with in a reasonable limit). So we can visualize that the energy, number of atoms and volume are fixed arbitrarily, and we let the other parameters change. What will be the temperature then?

[spin-1/2-nuclei]

Adiabatic compression was not a condition of the example. You have incorrectly assumed this to be the case. PV = nRT works just fine. The pressure was not specified; given the conditions you could solve for it. It's straightforward to do so.

 

I disagree, you've misunderstood the concept adiabatic compression as well as the ideal gas law. If you change the container size, you will change the volume. This change in volume will result in the change of pressure. Therefore you are incorrect, the two samples cannot have the same temperature because they cannot have the same kinetic energy.

 

You must use the concept of adiabatic compression because you have no external heat/energy source to account for the change. Thus, in the case of the smaller container, it is the work done on the system by the decrease in volume that results in the increase in energy, which is converted to kinetic energy, which in turn raises the temperature of the system as well as the pressure.

 

Even if you assume that the container expands to some degree - the containers are of identical composition - and are not the same size - thus your reasoning still falls apart. Container expansion would only impact how much of a change not if there was a change at all.

 

To prove this to yourself,

go take a tightly capped plastic bottle filled with air, get a vice grip from your garage and see if you can squeeze it until it pops off it's top or cracks in some other location. Then ask yourself, why did this happen? If you were to quantify the condition of the air molecules inside your bottle you'd see that you've not only increased the pressure by mechanically compressing the bottle with your hand, but you've also raised the temperature and as a result the kinetic/thermal energy, in addition to increasing the pressure - to the point of explosion/structural failure actually.

 

This is because if you compress the tightly capped bottle hard enough with the vice grips, an explosion or structural failure is exactly what you're going to get.

 

"Adiabatic heating occurs when the pressure of a gas is increased from work done on it by its surroundings, e.g. a piston. Diesel engines rely on adiabatic heating during their compression stroke to elevate the temperature sufficiently to ignite the fuel." - http://en.wikipedia.org/wiki/Adiabatic_process#Adiabatic_heating_and_cooling

 

Thus when all other things are created equal - the size of the container matters a lot.

 

Hope this helps..

Cheers

 

This I think implies that some extra energy is put into it. I think that the total energy of any system can be arbitrarily fixed; there is no restriction to the amount of energy that can be possessed (of course with in a reasonable limit). So we can visualize that the energy, number of atoms and volume are fixed arbitrarily, and we let the other parameters change. What will be the temperature then?

 

Hello,

 

No, there is no extra energy put into the system. The work comes from the force applied when changing the container size. This is how adiabatic compression works.

 

The only way you can change the temperature of a system is to change it's kinetic/thermal energy. A system can absorb energy and use it for many things, but if the temperature of the system increases then there must have been an increase in the kinetic/thermal energy. Now, there are situations when equilibrium can result in no observed change in energy, but that is not the case here. In the example you gave everything was fixed but the size of the container.

 

Hopefully this was helpful.

Cheers

Edited August 20, 2011 by spin-1/2-nuclei

[finiter]

No, there is no extra energy put into the system. The work comes from the force applied when changing the container size. This is how adiabatic compression works.

To be more clear, let me put forth it again: Both the containers contain the same energy, but the smaller one is at a higher temperature. Now, if we divide the energy of atoms as 'translational energy' and 'the rest', which part will be greater in each of the containers? (If 'translational energy' increases, 'the rest' has to decrease). Or, shall we divide it in some other way so that we can identify that a certain part of the energy causes an increase in temperature.

[spin-1/2-nuclei]

To be more clear, let me put forth it again: Both the containers contain the same energy, but the smaller one is at a higher temperature. Now, if we divide the energy of atoms as 'translational energy' and 'the rest', which part will be greater in each of the containers? (If 'translational energy' increases, 'the rest' has to decrease). Or, shall we divide it in some other way so that we can identify that a certain part of the energy causes an increase in temperature.

 

Hello,

 

What you're describing is impossible. You cannot keep the energy the same while changing one parameter and keeping the other's constant. This is because work must be done on the system to force the gas into the smaller container size. That decreases the volume of the gas, when that happens work must be done. The work is then converted to kinetic energy - which results in the increase in kinetic energy/thermal energy temperature and the increase in pressure.

 

To prove this to yourself, try the capped plastic bottle idea I suggest above.

 

Cap a 2liter plastic soda bottle tightly - an empty one - and then squeeze it as hard as you can with vice grips. You will see that when the container size decreases - i.e. - when you compress the gas - via the work applied to the system work will be done, which will then be converted to kinetic energy. Once that happens the temperature will increase. Once the temperature increase the pressure will increase.

 

If you continue squeezing you will eventually see that the bottle will explode or it will have a structural failure from the increase in pressure. If you take another 2 liter bottle and cap it and leave it on the counter whilst you squeeze the other bottle (i.e. make it smaller with the same amount of gas molecules in it as the unsqueezed 2 liter bottle) you will see that what you are suggesting is impossible..

 

So no external energy (i.e. heat source or light) is added to the system but changing the size of the container does work in the system. Which is converted to energy kinetic energy.

 

hope this helps..

Cheers

Edited August 20, 2011 by spin-1/2-nuclei

[Tom Booth]

View PostTom Booth, on 18 August 2011 - 06:44 PM, said:

If as you stated earlier that LIGHT IS heat then please explain how a laser can cool atoms to near absolute zero.

 

I didn't say "light is heat". I said the light from the sun is heat. It's a very important distinction —

 

Utter nonsense,

 

...the sun is emitting blackbody radiation because it's a thermal source and much hotter than its surroundings. A laser is not a thermal source — it emits a very narrow range of frequencies and is not at all like a blackbody.

 

More nonsense.

 

Tom Booth, on 18 August 2011 - 06:44 PM, said:

Sure, light carries energy that can, under certain circumstances be converted into "HEAT" (i.e. an increase in kinetic energy) but light is not heat.

 

 

At this point all I can do is point you to a physics textbook or class and suggest you pay attention to where they talk about the methods and details of heat transfer: conduction, convection and radiation.

 

Ummm...

 

I'm sure that if your absolutely ridiculous contentions are somewhere close to being within the sphere of some kind of REALITY outside of your IMAGINATION you could easily cite some online source and not use the above COP OUT.

 

First of all, I don't think light from the sun is somehow particularly somehow SPECIAL or DIFFERENT from light from other sources in the way you seem to think, though I can't really imagine in what way you think this might be.

 

Second of all, I don't think you actually understand the meaning of the term "Blackbody" of "Blackbody Radiation" if you imagine that the term applies only to the SUN or electromagnetic waves or Photons from the sun and not say - the heat lamp keeping the french fries warm in a fast food restaurant.

 

There is no TRANSFER of HEAT where a photon is flying through the vacuum of empty space. A photon is not HEAT whether it comes from the sun or anywhere else. There is no qualitative difference between an individual photon in a laser and an individual photon anywhere else in the universe to my knowledge.

 

You are just making stuff up as you go along IMO. Reaching for straws.

 

You imply by your above statements that light from the sun is "...a thermal source and much hotter than its surroundings". And, apparently mean to imagine that an ordinary incandescent light bulb is not "...a thermal source and much hotter than its surroundings".

 

You say

 

"A laser is not a thermal source — it emits a very narrow range of frequencies and is not at all like a blackbody"

 

Utter nonsense.

 

If a laser "is not a thermal source" than pray tell, how or why is it routinely used in various industrial applications for generating heat for cutting and welding ?

 

Anyway, "A thermal source" is not heat. Its a thermal source. The sun or a common light bulb are both "thermal sources". Light is light. Light is not Heat.

 

A photon or light in transit is not the same thing as a "heat transfer".

 

The "heat transfer" if any, takes place at the point of impact. Light itself, from the sun or anywhere else, viewed as a THING or OBJECT in isolation, is not "HEAT".

 

Unless of course you assume that light (or a photon) emitted from the sun is also absorbed by the skin of a sunbather on the beach instantaneously or emitted and absorbed simultaneously with no intervening transit through space or time.

 

Even if this were true, how would this be any different from a "sunbather" using artificial light in a tanning salon ?

 

Can you cite even one published source - online or otherwise ((i.e. in an actual textbook with an author and title and/or ISPN number so that the reference can be looked up)) in support of your amazingly silly contentions I have found objection to here ?

 

Like: "I didn't say "light is heat". I said the light from the sun is heat. It's a very important distinction — "

 

Says who?

 

Or: "A laser is not a thermal source — "

 

Says who ?

 

Or: "the sun is emitting blackbody radiation because it's a thermal source and much hotter than its surroundings."

 

You purport here to provide some kind of definition of "blackbody radiation" that matches up quite completely with nothing at all that I've ever read on the subject.

[swansont]

I disagree, you've misunderstood the concept adiabatic compression as well as the ideal gas law. If you change the container size, you will change the volume. This change in volume will result in the change of pressure. Therefore you are incorrect, the two samples cannot have the same temperature because they cannot have the same kinetic energy.

 

The example was two containers. Not one container undergoing expansion or contraction. There is no change in volume, there is a difference in volume.

 

Here is the situation (direct quote, emphasis added):

Suppose you have two containers, one larger than the other. Let each contain the same number of atoms of the same gas, and let their average kinetic energies be the same. In that situation, will the both have the same temperature?

 

V1>V2 n1=n2 And because the average KE's are the same, T1=T2 That's all that's given. There is no mention of a change in volume.

 

The only information that has any bearing on the answer is that the average KE's are the same. Everything else is a distraction. This actually sounds like a test question, where extra information is given. Some students will bend over backwards to use all of the information, and in doing so get the wrong answer. It's a pretty standard test-writing tactic.

 

I'm sure that if your absolutely ridiculous contentions are somewhere close to being within the sphere of some kind of REALITY outside of your IMAGINATION you could easily cite some online source and not use the above COP OUT.

 

http://en.wikipedia.org/wiki/Black_body

http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html

http://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html

 

First of all, I don't think light from the sun is somehow particularly somehow SPECIAL or DIFFERENT from light from other sources in the way you seem to think, though I can't really imagine in what way you think this might be.

 

Second of all, I don't think you actually understand the meaning of the term "Blackbody" of "Blackbody Radiation" if you imagine that the term applies only to the SUN or electromagnetic waves or Photons from the sun and not say - the heat lamp keeping the french fries warm in a fast food restaurant.

 

I used the sun as an example. I didn't say it was the only source of blackbody radiation.

 

There is no TRANSFER of HEAT where a photon is flying through the vacuum of empty space. A photon is not HEAT whether it comes from the sun or anywhere else. There is no qualitative difference between an individual photon in a laser and an individual photon anywhere else in the universe to my knowledge.

 

You don't feel warm when you go out and the sun shines on you? Ever notice how it cools off at night?

 

You imply by your above statements that light from the sun is "...a thermal source and much hotter than its surroundings". And, apparently mean to imagine that an ordinary incandescent light bulb is not "...a thermal source and much hotter than its surroundings".

 

Nope. Didn't say that about light bulbs. They are great thermal sources that happen to emit a little bit of visible light.

 

 

You say

 

"A laser is not a thermal source — it emits a very narrow range of frequencies and is not at all like a blackbody"

 

Utter nonsense.

 

If a laser "is not a thermal source" than pray tell, how or why is it routinely used in various industrial applications for generating heat for cutting and welding ?

 

You can raise the temperature via means other than heat transfer (as defined/used in physics). Photons have energy. You can raise the temperature of a piece of metal by bending it, too, but that's from doing mechanical work, not transferring heat. http://en.wikipedia.org/wiki/Work_(thermodynamics)

 

Can you cite even one published source - online or otherwise ((i.e. in an actual textbook with an author and title and/or ISPN number so that the reference can be looked up)) in support of your amazingly silly contentions I have found objection to here ?

 

If you go to Google and choose the "books" option, and type in "blackbody radiation" you get more than 400,000 hits. Here's College Physics, Volume 10 By Raymond A. Serway, Chris Vuille, Jerry S. Faughn

http://books.google.com/books?id=CX0u0mIOZ44C&pg=PA870&dq=blackbody+radiation&hl=en&ei=iCJQTuzGK8zq0QGEv-ClDw&sa=X&oi=book_result&ct=result&resnum=3&sqi=2&ved=0CDkQ6AEwAg#v=onepage&q=blackbody%20radiation&f=false

 

"Any object at any temperature emits electromagnetic radiation"

 

If you go to the next page they discuss the sun as one example, and how it emits thermal radiation.

[spin-1/2-nuclei]

@swansont

 

What you're saying is still incorrect. Its alarming that you think equal amounts of a gas in different size containers can be placed in any sized container & experience no changes between them.

 

For every action there is an equal and opposite reaction.

 

It doesn't matter when or how the gas is placed into a smaller environment, work must be done to compress gas. Though I suspect you may not know this, you are suggesting that any amount of gas can be compressed into any size container and no matter what container we check those gasses will always have the same temp.

 

Its obvious that what you're saying is wrong when you consider:

The fixed amount of gas cannot teleport itself into the smaller container, nor change the laws of physics to scale itself down accordingly.

 

I give up trying to reason with you. This is absolutely ridiculous.

[Cap'n Refsmmat]

What if the gas came in a pre-compressed bottle which had already cooled to room temperature?

 

I would again like to appeal to those posters using phrases like "Utter nonsense" and "absolutely ridiculous contentions" to follow SFN rule 1 more carefully.

[spin-1/2-nuclei]

What if the gas came in a pre-compressed bottle which had already cooled to room temperature?

 

I would again like to appeal to those posters using phrases like "Utter nonsense" and "absolutely ridiculous contentions" to follow SFN rule 1 more carefully.

 

If the gas is in a pre-compressed bottle the only way it will cool down to room temperature is if there is outgassing - thus changing the size of the sample.

 

People here are confusing the concept quantifying a fixed sample size across many different systems where the only thing changing is the size of the container - in which case by virtue of the situation their temperatures cannot be the same for all the reasons I've mentioned before.

 

and the concept of

 

Many different sized containers of different amounts of gas can be at the same temperature

 

or

 

a container that was at one temperature can cool down or heat up to another temperature if there is outgassing or if there is an external heat source.

 

For example, the cylinder of liquid nitrogen used for the laser in my lab remains the same really cold temperature while compressed inside the cylinder. That is to say it does not equilibrate and warm up to room temperature. That would be unfortunate for us.

 

Another example, is my argon tank, which loses gas - sent to my reactions via the Schelenk line - whenever I'm doing reaction and as a result it's temperature decreases because the volume increases as does the pressure as gas is let out of the system. The decrease in temp is the result of the decrease in kinetic energy - and the decrease in temp leads to a decrease in pressure.

 

Spray a can of something compressed and fill it get cooler to prove this to yourself.

 

I'm sorry, but I really don't know what else can be said on this issue to clear this up.

I've tried my best, but at some point bridges can't be built.

 

I really hope this helps, but if it doesn't I don't think there is anything else I can say.

Cheers

[Tom Booth]

spin-1/2-nuclei, on 20 August 2011 - 10:34 AM, said:

I disagree, you've misunderstood the concept adiabatic compression as well as the ideal gas law. If you change the container size, you will change the volume. This change in volume will result in the change of pressure. Therefore you are incorrect, the two samples cannot have the same temperature because they cannot have the same kinetic energy.

The example was two containers. Not one container undergoing expansion or contraction. There is no change in volume, there is a difference in volume.

 

This "Ideal" scenario being described above, IMO, would also be virtually "impossible" to arrive at under real world circumstances. If I'm wrong, please explain how such a condition might arise. How would one set up such an "experiment" to test this one way or the other ?

 

For example, using air as the "atoms" in the container.

 

To get "the same number of atoms" into each container, since "air" is more or less uniform everywhere on the earths surface, I would have to begin by somehow capturing air in two equal size containers and then expand one container to get the difference in volume.

 

I can think of no method for achieving the circumstance described without in some way doing some sort of "work" on the gas or otherwise manipulating the given or existing natural circumstances. Expand one container or shrink the other. Create a vacuum, put each container inside and release so much gas into each container....

 

Well, that last might work, maybe. lets see...

 

Perfect vacuum in both containers. Both inside a perfect vacuum. The vacuum acts as a perfect or near perfect insulator. All the atoms released start out at the same temperature. They may have to be filled SIMULTANEOUSLY in some way because if one is filled first, the tank or whatever from which the filling is taking place would have undergone some change in pressure and temperature.

 

The same number of atoms are. in such a fashion, released into each container. There is no other heat transfer in or out of either container. There is, presumably, some form of thermometers that can be read (and whos temperatures have been previously somehow equalized) already placed in each container before the vacuum was initiated in each container.

 

So now we're all set, we've filled each container and we read the thermometers,...

 

are the temperatures the same ?

 

I would say NO.

 

In the larger container the molecules have more room to move about and so collide with the thermometer less frequently.

 

So whatever your abstract concept about the ideal situation might be the actual temperature reading from the actual thermometers in such an experimental circumstance would IMO be different.

 

Not only the temperature, but also the pressure would be different. The pressure, from whatever source the containers were filled, would build up more quickly in the small container. The large container being larger, it would never achieve the same pressure as the small if filled with exactly the same number of atoms. The effect would be the same as expanding or contracting one container or the other.

 

Certainly I would think such an experiment would already have been carried out ages ago by some notable like Joules or Thompson.

 

Lets just make up a name shall we ?

 

Some guy back in 1702 with some ridiculous name like Guillaume Amontons did this experiment and lets call what he discovered "Amonton's Law" which states that "the pressure of a gas is directly proportional to its temperature" or something like that. Or maybe it was Charles or Boyle or Avogadro.

 

One of those guys I'm pretty sure has already done some such experiment.

 

Oh, wait, Guillaume Amontons is a real guy! sorry. Go figure.

 

http://en.wikipedia.org/wiki/Gay-Lussac%27s_law#Pressure-temperature_law

[swansont]

This "Ideal" scenario being described above, IMO, would also be virtually "impossible" to arrive at under real world circumstances. If I'm wrong, please explain how such a condition might arise. How would one set up such an "experiment" to test this one way or the other ?

 

Pump or compressor. Keep the volumes in a temperature bath, like ice water.

 

Some guy back in 1702 with some ridiculous name like Guillaume Amontons did this experiment and lets call what he discovered "Amonton's Law" which states that "the pressure of a gas is directly proportional to its temperature" or something like that. Or maybe it was Charles or Boyle or Avogadro.

 

One of those guys I'm pretty sure has already done some such experiment.

 

Oh, wait, Guillaume Amontons is a real guy! sorry. Go figure.

 

http://en.wikipedia.org/wiki/Gay-Lussac%27s_law#Pressure-temperature_law

 

Oh, wait, Guillaume Amontons is a real guy! sorry. Go figure.

 

http://en.wikipedia.org/wiki/Gay-Lussac%27s_law#Pressure-temperature_law

 

"The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas's absolute temperature."

 

A pity you didn't actually read the link. It was the second sentence in that section. The example under discussion does not refer to containers of equal volume.

 

Go take a physics class. Please.

 

@swansont

 

What you're saying is still incorrect. Its alarming that you think equal amounts of a gas in different size containers can be placed in any sized container & experience no changes between them.

 

For every action there is an equal and opposite reaction.

 

It doesn't matter when or how the gas is placed into a smaller environment, work must be done to compress gas. Though I suspect you may not know this, you are suggesting that any amount of gas can be compressed into any size container and no matter what container we check those gasses will always have the same temp.

 

I did no such thing. I stated that for the specific conditions of the example, that the temperatures were equal.

 

Its obvious that what you're saying is wrong when you consider:

The fixed amount of gas cannot teleport itself into the smaller container, nor change the laws of physics to scale itself down accordingly.

 

I give up trying to reason with you. This is absolutely ridiculous.

 

The example did not dictate how the samples were prepared. Are you really insisting that you can't have V1 at P1 and V2 at P2, with n1=n2 and T1=T2? Really? There is NO way to arrive at that condition? It should be trivial to show this. If the answer is impossible, the ideal gas law should be be unable to be solved to give a physical answer (e.g. the solution is a negative term). Since I'm obviously unable to do this, please show me.

[Tom Booth]

What if the gas came in a pre-compressed bottle which had already cooled to room temperature?

 

"Pre-compressed" is still compressed. Cooled is still cooled.

 

If I leave a pan of water that I heated up on the stove to cool it does not prove that it was never heated.

 

Certainly, containers, (whatever they might be filled with, or how much) will eventually equalize in temperature, (even containers of different size that contain the same number of atoms, presumably) if exposed to some source of heat like ambient temperature air.

 

Even if I compress gas into one container; like an air compressor tank, the hot compressed air will eventually cool to room temperature, but in the process of cooling the gas will give up energy, which can be proven if it is released back to atmospheric pressure. When released the gas will be colder than it was before being compressed, which is the basic principle behind refrigeration.

 

Compress at ambient -> (temperature increases) -> allow thermal equalization with ambient while under pressure -> release -> temperature decreases.

 

You can imagine that some such thermal equalization never took place, that no heating or cooling ever took place, that no compression or expansion or contraction or whatever ever took place, that these containers appeared ex ex nihilo in such a state by divine fiat or something. and you just ended up with the final result of "pre-compressed bottles already cooled to room temperature" well OK.

 

I would again like to appeal to those posters using phrases like "Utter nonsense" and "absolutely ridiculous contentions" to follow SFN rule 1 more carefully.

 

 

OK, if others, including yourself, will adhere more closely to rule #4

 

"The use of logical fallacies to prove a point is prohibited."

 

Can I say that the scenario you describe "pre-compressed bottle which had already cooled to room temperature?" without accounting for or while ignoring the obvious compression, heating, cooling, expansion, pressure changes etc. that must have taken place is a logical fallacy ?

[mississippichem]

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heat.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html

 

"Heat may be defined as energy in transit from a high temperature object to a lower temperature object. An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is properly called heating."

 

I think this is the best definition of heat posited thus far in the thread. One could substitute the word temperature for "average kinetic energy" [imath] \frac{3}{2}NkT [/imath](ideal monoatomic gas), to avoid the confusion inherent with temperature. I would include [imath] dU=dq [/imath] at constant V and no additional W, and [imath] dH=dq [/imath] at constant P with no additional W to contrast how heat is not internal energy or enthalpy. I think it is also telling that no one ever sees a [imath] \Delta q [/imath] written down in thermo equations as it would be redundant.

 

Much of this discussion I think stems from miscommunication and as already stated, "sloppiness" in the thermodynamic lexicon. "Heat" as a verb should be replaced.

Edited August 21, 2011 by mississippichem

[DrRocket]

This is the part that's wrong. If you have to objects at the same temperature, no heat will flow. However, the objects have a temperature and thermal energy.

 

One of the big problems in all of this is that someone decided to call C the heat capacity, and that leads to certain conceptual errors.

 

http://hyperphysics....mo/heat.html#c1

http://hyperphysics....rmo/heatra.html

 

"Heat may be defined as energy in transit from a high temperature object to a lower temperature object. An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is properly called heating."

 

Meanwhile, in physics, heat is as is defined in the hyperphysics links I just gave.

 

This is correct. It is also a matter of definition, and arguing about definitions is futile.

 

There are, of course, meanings that lie outside of physics, but this is a physics forum.

 

http://www.nba.com/heat/

[Cap'n Refsmmat]

If the gas is in a pre-compressed bottle the only way it will cool down to room temperature is if there is outgassing - thus changing the size of the sample.

So if I compress a bottle of gas, and it becomes warmer due to the increase in pressure, it will never cool down unless the valve leaks?

 

For example, the cylinder of liquid nitrogen used for the laser in my lab remains the same really cold temperature while compressed inside the cylinder. That is to say it does not equilibrate and warm up to room temperature. That would be unfortunate for us.

So how long will this cylinder of liquid nitrogen remain cold? Indefinitely?