Temperature of Gas: What's Happening to Atoms/Molecules?

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    Gas Temperature
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Discussion Overview

The discussion centers on the behavior of gas molecules in relation to temperature changes during compression and expansion. Participants explore the kinetic energy of gas particles and the implications of work done on the gas, addressing both theoretical and conceptual aspects of gas behavior.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that compressing a gas increases its kinetic energy, leading to a rise in temperature, while expanding the gas results in a loss of kinetic energy and a decrease in temperature.
  • Others argue that the temperature change during expansion or compression can depend on the forces applied, suggesting that if the force exerted on the gas during expansion is greater than the expansion force, the temperature drop may be minimal.
  • A later reply questions the necessity of heating during compression, referencing the ideal gas law and suggesting that isothermal processes could occur.
  • One participant clarifies that gas molecules do experience acceleration or deceleration during compression and expansion, likening it to a ping-pong ball bouncing off a moving paddle.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between work done on a gas and temperature changes, with no consensus reached on the necessity of temperature increase during compression or the conditions under which it occurs.

Contextual Notes

Some statements rely on assumptions about the ideal behavior of gases and may not account for real-world complexities, such as the effects of varying forces during expansion and compression.

Drakkith
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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?
 
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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)
 
vorcil said:
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)

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

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
 
Drakkith;2904417 I can't see them somehow being accelerated or decelerated through compression/expansion said:
They ARE accelerated or decelerated during compression or expansion. Think of compressing the gas with a piston. The piston is moving inward, so each time a molecule of the gas hits the piston, it speeds up a little, just like a ping-pong ball bouncing off a paddle that is moving towards it. When the gas is expanded, the piston is moving away from the gas, so the gas molecules slow down a little each time they bounce off it.
 
Drakkith said:
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?

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

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