# Homework Help: Find out Cp of the gas

1. Apr 14, 2014

### utkarshakash

1. The problem statement, all variables and given/known data
4.48 L of an ideal gas at STP requires 12 cal to raise the temperature by 15°C at constant volume. The Cp of the gas is (in cal)?

3. The attempt at a solution

ΔU = nCvΔT
I can find out C_v from above equation but how to get C_p? I assume it would be wrong to use this equation ΔQ=nCpΔT as the process is carried out at constant volume and not pressure.

2. Apr 14, 2014

### Saitama

You said you can calculate $C_v$ (and btw, it comes out to be a nice integer, keep everything in cal). Do you know of a relation between $C_v$ and $C_p$?

3. Apr 14, 2014

### utkarshakash

I did use that relation earlier but since the question is an integer type(you know what they mean,don't you?) it won't give me an integral answer(rounding off the digits still gives an answer beyond the range :yuck:).

4. Apr 15, 2014

### Saitama

May I know which relation did you use?

I should have said to use a relation between $C_v$ and degrees of freedom. You should be able to calculate $C_p$ once you have the degrees of freedom.

5. Apr 15, 2014

### utkarshakash

Cp-Cv = R

The question does not state the nature of gas. So degrees of freedom is not known.

6. Apr 15, 2014

### Saitama

So what did you plug in for Cv? Note that it should be in cal. And what is the value of R in calorie units?

7. Apr 24, 2014

### rohit1994

R = 1.9872041 cal/K/mole
and Cv you can calculate from ΔU = nCvΔT.
the put Cp-Cv = R