# Homework Help: Thermodynamics. Finding specific heat capacity

1. Nov 6, 2013

### Rugile

1. The problem statement, all variables and given/known data

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.

2. Relevant equations

W=pΔV=nRΔT
Q=nCvΔT

3. 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?

2. Nov 6, 2013

### Staff: Mentor

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

3. Nov 7, 2013

### Rugile

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

4. Nov 7, 2013

### Staff: Mentor

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.

5. Nov 7, 2013

### Rugile

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.