# Temperature of a Gas

1. Sep 27, 2010

### Drakkith

Staff Emeritus
I'm a little confused on the temperature of a gas. If gas is heated when compressed, and cools when it expands, what is happening to the atoms/molecules of the gas itself? I can't see them somehow being accelerated or decelerated through compression/expansion, so is it a question of how much gas is in a certain point in a given amount of time or something?

2. Sep 27, 2010

### vorcil

When a gas is being compressed you are putting work into compressing it, this is turned into a higher kinetic energy for the gas (i.e higher temperature)

so whether you heat the gas, compress it or both, the temperature will increase,

likewise when the gas is expanding, the particles are doing work on the chamber by colliding with it, and increasing the volume, so they loose kinetic energy (i.e cool down)

3. Sep 27, 2010

### Drakkith

Staff Emeritus
Even if you are the one that causes it to expand? Like tugging on a piston to make the chamber larger?

4. Sep 27, 2010

### vorcil

It would depend,

If the tug used more force than the expansion force, it would still loose temperature but the temperature drop would be very small

if the gas was extremely hot, the effect of someone tugging on it would be very small compared to the expansion force

also the rate/change of expansion/compression effects the temperature change

5. Sep 28, 2010

### phyzguy

6. Sep 28, 2010

### Andy Resnick

Why does the gas *have* to heat up when it's compressed? P1V1 = P2V2 is isothermal.

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