# Gas temperature increase by pressure

1. Dec 12, 2012

### Flor

Hi,

May I ask you, i have a question about gases. Take a gas and give it under high pressure conditions. Then immediately give the same gas under no pressure conditions (some free space). Then my question is what will happen to the temperature of this gas? Can we observe the increase in temperature?

My idea behind this problem is connected with kinetic energy of gas particles. When you make a solid matter from a gas (gas is under very high pressure), then the particles are very close to each other. It is hard to move for these particles. Then you put this solid matter into the no pressure conditions. It will expand. The particles will start to move. Their kinetic energy will be higher. So the temperature will also be higher (maybe hundreds or thousands degrees of Celsius for some materials) for some time. We can compare it to a prisoner in a prison. If you open the prison, then there might be a hell.

Best,
Flor

2. Dec 13, 2012

### daveyrocket

No, high pressure doesn't mean low kinetic energy. Kinetic energy is directly related to temperature, not pressure (it also doesn't depend on the phase of matter). Your "prisoners" in your prison are bouncing off the walls when they're locked up... when you open the gates they move just as fast as they were before, there just aren't any walls to bounce off of.

For a real answer to your question, it depends. For an ideal gas, there is no change in temperature if you go through free expansion. The typical case for a real gas is to cool somewhat due to attractive interactions between the atoms/molecules which are relevant at high pressures. But there are some cases where gases heat up under free expansion. (hundreds or thousands of degrees C is *way* beyond the real scale though). For more information, see here: http://en.wikipedia.org/wiki/Jouleâ€“Thomson_effect