.Verifying Heat Capacity at Constant Pressure and Volume

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Discussion Overview

The discussion revolves around the understanding and verification of heat capacity at constant pressure and volume, exploring the conditions under which temperature changes occur in a system. Participants examine the relationships between heat transfer, temperature, pressure, and volume in various scenarios.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that for a system to experience a rise in temperature, either pressure or volume must remain constant, implying that expansion during heat transfer prevents temperature increase.
  • Another participant counters that heating a gas will lead to increases in both volume and pressure, and that it is possible to impose conditions on either variable, allowing for temperature increases without both being constant.
  • A further contribution states that heating can occur regardless of constraints on volume or pressure, unless the system is required to maintain a constant temperature.
  • One participant provides an example of a nearly-empty bag of air, stating that heating it results in an increase in temperature while allowing for expansion at constant pressure.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for temperature increases in relation to heat capacity, with no consensus reached on the initial claims regarding constant pressure and volume.

Contextual Notes

Participants have not fully resolved the implications of their statements regarding the definitions and conditions of heat capacity, nor have they clarified the specific scenarios under which temperature changes occur.

grscott_2000
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Can someone confirm if my understanding of heat capacity is correct - particulary at constant volume and pressure?

My understanding is that for a system to experience a rise in temperature either its pressure or its volume must remain constant. If either of these is allowed to expand naturally when heat is transferred to it then there will be no rise in temperature
 
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When you heat a mass of gas it will increase in volume AND/OR pressure. You can force the volume or pressure to be constant, but not both. But you can also impose any behavior to volume or pressure. You impose it by external means.
A system can experience a rise in temperature with neither the volume nor pressure remaining constant.
There are even very common processes called "adiabatic" where temperature, pressure and volume change simultaneously.

But heat capacity coefficients are only defined for constant pressure or constant volume processes. Two is enough!
 
You can always heat something up.
It does not matter if you contrain it to keep its volume, or its pressure, or its shape, or its color, or its elasticity, or anything ...

Except of course if you decide that your system must keep its temperature constant.

I assume that by "heat up" you meant "increase temperature".
 
Take the case of a nearly-empty bag of air. The air occupies a certain volume and when you apply heat to it, it's temperature increases and it also expands, while the pressure remains constant.
 

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