Thermo Chemistry: Explaining Cp vs Cv

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Discussion Overview

The discussion revolves around the concepts of heat capacity at constant pressure (Cp) and constant volume (Cv) in thermochemistry. Participants explore the implications of these definitions and the behavior of gases under different conditions, including the relationship between heat, pressure, and volume.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how heat added at constant pressure can be used for expansion, noting that expansion typically involves a change in pressure.
  • Another participant explains that when a substance is heated at constant pressure, it must expand to maintain that pressure, implying that some of the heat contributes to work done during expansion.
  • A participant raises a question about the difference between expansion and inflation of gas, seeking clarification on terminology.
  • Another participant responds that they see no difference between expansion and inflation, suggesting a lack of distinction in the context of the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between heat, pressure, and volume, indicating that there is no consensus on the nuances of these concepts. The discussion remains unresolved regarding the specific terminology and implications of expansion versus inflation.

Contextual Notes

Some assumptions about the definitions of heat capacity and the behavior of gases under constant pressure and volume conditions are not fully explored. The discussion does not clarify the mathematical relationships involved or the conditions under which these concepts apply.

zorro
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This is a statement in my book 'The heat capacity at constant pressure Cp is generally larger than that at constant volume Cv because at constant pressure, a part of heat added to the substance may be used in work of expanding whereas at constant volume all the added heat produces a rise in temperature'. I did not understand these two things-

At constant pressure, how can heat added be used for expanding (since expanding leads to change in pressure).

At constant volume what if the added heat expands the gas?
 
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If you heat something it usually inflates, to keep the pressure constant it has to expand.

In constant volume heated gas WANTS to expand - but as the volume is kept constant, it is impossible, so instead the pressure goes up.

--
 
what is the difference between expansion and inflation of gas?
 
None as far as I am concerned, sorry if it sounded as there is a difference.
 

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