temperature of steam

[fermions]

If we boil a beaker of water, then we put a thermometer above the surface... that is, we are checking the temperature of steam and we always get 100 degrees Celsius under normal pressure right?

so is it possible to have steam over 100 degrees? how about we collect the steam and then heat it up is it still 100 degrees?

thanks

[YT2095]

at 101kpa steam will be 100c, above that (like in a pressure Cooker) steam can be well above 100C called "super heated" steam.

 

that`s why pressure cookers take less time to cook than ordinary boiling or steaming

[Asimov Pupil]

it's the same deal with ice when you melt it, it stays at 0 degrees until it is all melted then it rises in tempurature so you have to convert all the potential energy of the boiling water to kinetic energy of steam before it can rise in temurature

[fermions]

so under normal pressure steam is always 100 degrees right?

so like steam above water surface it's always 100C as it's an open system am I correct?

[YT2095]

correct if we take "Normal Pressure" to mean 1 atmosphere

[fermions]

thanks a lot now I understand...

[jdurg]

Steam can be well above 100 degrees C. It normally forms at 100 degrees, but if the surroundings are hot enough it can be well above that. If you boil water in a gigantic chamber so that the air pressure remains at 1 atmosphere, if you provide enough heat to that chamber you can increase the temperature of steam much higher than 100 degrees.

 

Like with ice, if it's cold enough the temperature of ice will be well below 0 degrees. Put some water in liquid nitrogen. I guarantee you that the ice's temperature will be below 0 degrees.

 

Asking what the temperature is of steam is like asking what's the temperature of water, or what's the temperature of iron.

[YT2095]

Jdurg, although I agree with you that steam can be almost any temp (to a certain point), in his experiment with plain water in a beaker at 101kpa, will not exceed 100c.

 

if he`de got and Oxy-Hydrogen torch things would be different

[swansont]

And remember that you can't see steam. If you measure the temperature of the cloud you can see above the beaker (or whatever) that's water that has begun to condense and will probably be cooler.

[YT2095]

yup, steam is a Gas. the part you can see is water vapor, and not steam.

[Asimov Pupil]

Hey I learned all this in Chemistry isn't this suposed to be physics?

[YT2095]

it`s one of those subjects (like batteries) that are covered in both Physics and Chem, they often overlap at the begining

[mezarashi]

Jdurg' date=' although I agree with you that steam can be almost any temp (to a certain point), in his experiment with plain water in a beaker at 101kpa, will not exceed 100c.

 

if he`de got and Oxy-Hydrogen torch things would be different [/quote']

 

I'm going to have to disagree with this. I remember that steam can definitely go beyond 100 degrees at atmospheric pressure 101kpa. The change in phase is affected by the pressure and temperature, but this does not impose a limit on temperature. Any Thermodynamics textbook at college level will clearly show a phase diagram that supports this.

 

Pressure cookers work by increasing the pressure, thus increasing the temperature in which water boils, and that steam forms, so in effect you have your food being exposed to a higher temperature liquid/vapor. However, given constant pressure, it is absolutely normal for steam to go above 100 degrees (superheated vapor-won't condense into liquid water anytime soon). It will just form at 100 degrees(just about to vaporize-saturated liquid, just about to condense-saturated vapor), but there is no limit for its temperature to rise. Same goes for ice. Ice will form at 0 degrees at 1 atm, but it doesn't mean that it can't go down to say -20.

 

A simple thought experiment. How cold do you think the ice in Antartica is when the air temperature is -60 degrees? If you keep heating steam and you it's temperature doesn't increase, where does all it's energy go? We all know substances when hot enough can ionize. If steam can never get that hot, then it's a non-ionizable substance? Just a quote for thought

 

Edit note: Temperature you read on a thermometer reads "average temperature", so even if you read 100 degrees, there will actually be bits that are hotter than this, and bits that are cooler.

[swansont]

I'm going to have to disagree with this. I remember that steam can definitely go beyond 100 degrees at atmospheric pressure 101kpa. The change in phase is affected by the pressure and temperature' date=' but this does not impose a limit on temperature. Any Thermodynamics textbook at college level will clearly show a phase diagram that supports this.

 

Pressure cookers work by increasing the pressure, thus increasing the temperature in which water boils, and that steam forms, so in effect you have your food being exposed to a higher temperature liquid/vapor. However, given constant pressure, it is absolutely normal for steam to go above 100 degrees (superheated vapor-won't condense into liquid water anytime soon). It will just form at 100 degrees(just about to vaporize-saturated liquid, just about to condense-saturated vapor), but there is no limit for its temperature to rise. Same goes for ice. Ice will form at 0 degrees at 1 atm, but it doesn't mean that it can't go down to say -20.

 

A simple thought experiment. How cold do you think the ice in Antartica is when the air temperature is -60 degrees? If you keep heating steam and you it's temperature doesn't increase, where does all it's energy go? We all know substances when hot enough can ionize. If steam can never get that hot, then it's a non-ionizable substance? Just a quote for thought

 

Edit note: Temperature you read on a thermometer reads "average temperature", so even if you read 100 degrees, there will actually be bits that are hotter than this, and bits that are cooler.[/quote']

 

YT limited his analysis to the open beaker, so there is no source of energy to superheat the steam. It will be at 100 C at 1 atm.

 

"Average temperarue" is a bit of a misnomer as you've used it. Temperature is a measure of the average kinetic energy of the particles, and that will vary, since they will have a distribution of energies. Certainly some molecules will have a much higher energy than others, but temperature is the property of an ensemble of atoms or molecules.

 

Certainly two parts of a material can be at different temperatures, and if that scale is the size of your probe you may be averaging the values, but that also means the system is not in thermal equilibrium. For a gas, that means the the molecules aren't colliding with each other and/or you have a heat source that gives you a temperature gradient. For the case in question, I don't think either applies. The steam rises through the water in bubbles, so there is no heat source, and given the relatively high speed of the molecules, they are certainly undergoing many collisions and will be in thermal equilibrium when they are released at the surface of the water.

[fermions]

I would like to ask about the difference between water vapour and steam.... is water vapour what steam has condensed? and can we see steam if it is a gas?

[swansont]

I would like to ask about the difference between water vapour and steam.... is water vapour what steam has condensed? and can we see steam if it is a gas?

 

If you can see it, it has already condensed into droplets of multiple molecules. You cannot see steam.

[Asimov Pupil]

Water vapour is the result of a reaction also right?

[YT2095]

Water vapour is the result of a reaction also right?

 

I`m not 100% certain what you mean by "a Reaction" here?

 

steam is a Gas that relies upon thermal activity or negative pressure below 101kpa.

for example water will boil at a lower temperature on the top of a mountain than it will on your boat in the Ocean

 

again though, water vapor can be within a range of temperatures also, Clouds are quite cold, and the white(ish) vapor you see from a boiling kettle can still burn you!

both are the same, just different temperatures and presures.

 

Steam on the other hand you cannot see anymore than you can see the air around you

[Asimov Pupil]

a chemical reaction can also produce water vapour

[YT2095]

sure, there`s a few that will do that

 

each time you burn a hydrogen containing gas in air, water is often a product.