Thermodynamics. Finding specific heat capacity

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Discussion Overview

The discussion revolves around a thermodynamics problem involving an ideal gas expanding with a constant molar heat capacity, where participants seek to determine the specific heat capacity (Cx) based on given work and heat quantities. The scope includes theoretical reasoning and problem-solving related to heat capacities and gas behavior.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Rugile presents a problem involving an ideal gas with a constant molar heat capacity during expansion and attempts to derive Cx from the equations related to work and heat.
  • Rugile assumes the first process is isobaric based on the work done and the temperature change, questioning the nature of the first process.
  • Chet questions the completeness of the problem statement, asking for clarification on whether the expansion is adiabatic and reversible, and whether the number of moles is specified.
  • Rugile expresses uncertainty about the correctness of their solution and the implications of the constant molar heat capacity on the nature of the first expansion.
  • Another participant suggests that the constant molar heat capacity does not preclude the possibility of the process being adiabatic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the first expansion process or the completeness of the problem statement. There are multiple viewpoints regarding the assumptions made about the gas behavior and the implications of the given information.

Contextual Notes

There are limitations regarding the assumptions about the type of expansion and the lack of information on the number of moles of gas, which may affect the analysis.

Rugile
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Homework Statement



Ideal gas of point particles is expanding so that its molar heat capacity Cx is constant and the work done by gas is W = 156J. Then the gas is isochorically heated to the initial temperature by receiving the quantity of heat which is Q = 125 J. Find Cx.

Homework Equations



W=pΔV=nRΔT
Q=nCvΔT

The Attempt at a Solution



So first of all, we know that the second process is isochoric. Though we don't know the type of first process. Yet it can't be isochoric, because the work done is not equal to 0. It is also not isothermic, because there is a temperature change. So the first process is isobaric and the molar heat capacity we're looking for is Cp. I managed to derive from the two equations that Cv = A / (QR). Aaand I'm stuck. How do I connect the two molar heat capacities? Are my attempt at solution and assumptions correct?
 
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Hi Rugile. Welcome to Physics Forums.

There seem to be some omissions from the problem statement. Is this the exact wording of the problem statement, or is it your interpretation? Is any mention made of the number of moles of gas? Is any mention made that the first expansion is adiabatic and reversible? Please write out the problem statement exactly as it appears in your book (or whatever).

Chet
 
Hi and thank you for the greeting :)

This problem statement is in fact translated, though nothing seems to be omitted. Nothing mentioned about the expansion being reversible. Is it incorrect to assume that the first expansion can't be adiabatic as the molar heat capacity during the first process remains constant?

I doubt the original statement would be any help as it was translated. Also I'm pretty sure this is the all information we get from the statement - no moles of gas, nothing else. Is my solution provided in first post incorrect?

Rugile
 
Rugile said:
Hi and thank you for the greeting :)

This problem statement is in fact translated, though nothing seems to be omitted. Nothing mentioned about the expansion being reversible. Is it incorrect to assume that the first expansion can't be adiabatic as the molar heat capacity during the first process remains constant?

I doubt the original statement would be any help as it was translated. Also I'm pretty sure this is the all information we get from the statement - no moles of gas, nothing else. Is my solution provided in first post incorrect?

Rugile
I don't know. We must have lost something in the translation. Incidentally, just because the molar heat capacity is constant doesn't mean that the process isn't adiabatic.
 
Chestermiller said:
I don't know. We must have lost something in the translation. Incidentally, just because the molar heat capacity is constant doesn't mean that the process isn't adiabatic.

Well we also know that the gas is made up of single (individual) atoms. But we don't know what atoms. Nothing can be lost, I checked it like a hundred times.
 

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