Enthalpy and Entropy

[bcraig]

This is my homework question:

 

Explain the principles of heat energy transfer from one body to another with reference to the following terminology. Temperature difference, Enthalpy, Entropy, Coefficient of heat transfer, Specific heat transfer, Conduction, Convection, Radiation.

 

This is my first week in this class and basically I have had no previous education in this field of thermodynamics or anything related really =S Please my excuse my stupidity.

 

In this forum question I just want to cover Entropy and Enthalpy.

This is what I have written so far and I am not sure if I even totally understand this.

 

 

When heat energy is changing, scientists normally measure the change in enthalpy rather than the change in energy.
“Enthalpy is the thermodynamic function that accounts for heat flow in processes occurring at constant pressure when no forms of work are performed other than P-V work (pressure-volume).”
A chemical reaction can cause a substance to become warmer or colder. This allows heat to flow out to surrounding matter or flow heat in from surrounding matter until the temperature is equal. If the pressure is constant then this amount of heat flow will express how much the enthalpy changed. If a chemical reaction gives off heat, then the enthalpy of the reaction is said to have decreased. The measure of energy which is unavailable to do work is called entropy and where enthalpy has decreased then entropy has potentially increased.

 

My questions:

1) ... struggling. Is this enough for a very very basic description?

2) Does this example so vaguely true?..

If I compress a spring, I am using the energy in my body which decreases my internal enthalpy and increased the universe entropy. The spring has an increase in enthalpy as it has the potential to string back. The amount of energy I have used to compress that spring may not be the the same quantity of energy passed to the spring as some of the energy has been exhausted to things such as the noise of the spring moving, and the temperature increase from pressure...

 

 

 

When a process occurs at constant pressure, the heat evolved (either released or absorbed) is equal to the change in enthalpy. Enthalpy (H) is the sum of the internal energy (U) and the product of pressure and volume (PV) given by the equation of:

H=U+PV

 

 

3) I don't understand "the product of pressure and volume." What is the product?

4) What is the internal energy? Is that like the amount of energy that will be exhausted from the potential for a compressed spring to uncompress?

[Endy0816]

1) I would say so.

2)

 

The amount of energy I have used to compress that spring may not be the the same quantity of energy passed to the spring as some of the energy has been exhausted to things such as the noise of the spring moving, and the temperature increase from pressure...

 

I would stick with this bit for learning purposes.

 

3) Product in math simply means the result of multiplication(PV).

 

4) Basically, though I would suggest thinking in terms of a compressed gas, rather than a spring.

[studiot]

 

3) I don't understand "the product of pressure and volume." What is the product?

 

The product is mechanical work.

 

bcraig,

Please fill in some background on for us - tell us where you are coming from in terms of Science. These are enormous questions to answer even with sufficient physics background.

 

I seriously suggest you do not start with enthalpy and entropy, but work through your list in reverse order.

Conduction, convection and radiation are much easier to understand and should be tackled first. I suspect you already have some understanding of this part.

Doing this will have the advantage of building up your store of knowledge and success.

Work from what you already know to what you want to learn, not the other way round.

 

In particular do you understand

 

1) What energy is and in particular 'heat energy'?

 

2) My answer to your specific question (3) above about mechanical work?

 

It is impossible to approach the rest of your question without this understanding.

 

Finally you have duplicated your question.

This makes for communication difficulties.

 

Please keep it all in one place.

 

But rest assured, plenty of help is available here.

 

[bcraig]

Endy0816,

Thank you for your input =)

 

 

 

studiot,

I feel I have a reasonable understanding of conduction, convection and radiation. And I wasn't too bothered about enthalpy and entropy. I really just wanted a bit of confirmation that I was roughly close.

I am studying to be a process operator in the petrochemical industry and we have just a small assignment on the basics of chemistry and thermodynamics.I don't think I need a thorough understanding of the topic but just a simple understanding.

 

Did you delete my other topic related to the same question? That was really my main concern regarding specific heat and heat transfer coefficient...

They are the final points that I am trying to understand how they relate to my homework question.