What Happens to Internal Energy in a Piston if Pressure is Increased?

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Discussion Overview

The discussion revolves around the behavior of internal energy in a piston when pressure is increased while maintaining constant temperature. Participants explore the implications of the ideal gas law and the first law of thermodynamics in this context.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that for an ideal gas, internal energy is solely a function of temperature, implying that if temperature remains constant, internal energy does not change.
  • Others discuss the relationship between pressure, volume, and work done on the system, suggesting that increasing pressure while keeping temperature constant requires heat to be removed from the system.
  • There is a question raised about whether the internal energy decreases due to heat transfer to the surroundings, with some participants expressing confusion about this concept.
  • One participant distinguishes between ideal and non-ideal gases, suggesting that changes in pressure for non-ideal gases could affect internal energy differently.
  • Another participant confirms that an ideal gas will expand if pressure decreases while keeping temperature constant, reiterating that internal energy remains constant under these conditions.

Areas of Agreement / Disagreement

Participants generally agree that for an ideal gas at constant temperature, internal energy remains constant despite changes in pressure. However, there is some disagreement regarding the implications for non-ideal gases and the interpretation of heat transfer and work done on the system.

Contextual Notes

Participants express uncertainty regarding the differences between ideal and non-ideal gases, and how these differences might affect internal energy under varying conditions of pressure and volume.

Smileyxx
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If the temperature is kept constant,what happens to internal energy if the pressure is increased in piston?
 
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I believe that in this situation you'd make use of the ideal gas law.
 
Smileyxx said:
If the temperature is kept constant,what happens to internal energy if the pressure is increased in piston?

For an ideal gas, the internal energy is a function only of temperature. If the temperature is kept constant, the internal energy is constant. From the first law, this means that the heat added is equal to the work done on the surroundings. If the pressure increases, that means that the volume is decreasing, and the surroundings are doing work on the system. This means that an equal amount of heat must be removed from the cylinder (in order to maintain constant temperature).
 
So am i suppose to mean that the internal energy decreases because of transfer of the heat to surrounding?
 
Smileyxx said:
So am i suppose to mean that the internal energy decreases because of transfer of the heat to surrounding?
It is being kept at a constant temperature - by your definition in the OP. Increasing the pressure involves doing work but the temperature (average KE) is being kept constant so that must mean that the added energy must be taken away by the surroundings.
Is this counter-intuitive?

I'm only repeating what's in the earlier post but you seemed to be questioning it.
 
sophiecentaur said:
It is being kept at a constant temperature - by your definition in the OP. Increasing the pressure involves doing work but the temperature (average KE) is being kept constant so that must mean that the added energy must be taken away by the surroundings.
Is this counter-intuitive?

I'm only repeating what's in the earlier post but you seemed to be questioning it.

Ya that's what my question is. Is it correct?
 
Two people have told you the same thing. Have you a good reason not to believe it? Show us your reasoning.
 
sophiecentaur said:
Two people have told you the same thing. Have you a good reason not to believe it? Show us your reasoning.

I was just confused between ideal and normal gas.So for ideal gas with constant temperature ,pressure falls or rise doesn't make difference but if its not ideal gas ,pressure fall may expand volume so their is greater internal energy and vice versa? Is their any mistake in this statement?
 
Smileyxx said:
So for ideal gas with constant temperature ,pressure falls or rise doesn't make difference but if its not ideal gas ,pressure fall may expand volume so their is greater internal energy and vice versa?

An ideal gas will also expand if the pressure is decreased while keeping the temperature constant. But the internal energy is constant, since temperature is constant, by your assumption.
 
  • #10
torquil said:
An ideal gas will also expand if the pressure is decreased while keeping the temperature constant. But the internal energy is constant, since temperature is constant, by your assumption.

Yeah i get it now.thanks :smile:
 

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