# Homework Help: Thermal Expansion of Gas - am I on the right track?

1. Oct 13, 2009

### Quelsita

Question:
One mole of an ideal gas with cv=2.5R, initially at 0.0degC, is heated at constant pressure. How much heat is needed to double its volume?

Solution:

Know:
n=1
T0=273.15K
cv=2.5R
$$\Delta$$P=0
Vf=2V0

H=U +PV
and thus, Q= $$\Delta$$H
Q=ncv$$\Delta$$T

We can rearrange to find
$$\Delta$$H=$$\Delta$$U +P(2V0-V0) -> since Vf=2V0

My question is, what do I do with the internal energy? and how can I find the pressure with the given information if I also don't know the final temp?

2. Oct 13, 2009

### Mapes

Hint: it's an ideal gas.

3. Oct 13, 2009

### Quelsita

Well, for an ideal gas PV=nRT.
And since P is constant, can I say that:

P0 = (nRT0)/V0
is the same as
P= (nRT0)/V0

so , P= [(273.15K)(nR)]/V0

4. Oct 13, 2009

### Mapes

What's the final temperature?

5. Oct 13, 2009

### Quelsita

Honestly, I'm kinda stuck here. It feels to me like with the information I have that I'm just going in circles using one equation to solve another one.
I don't think this question should even be this confusing...

6. Oct 14, 2009

### Mapes

Use the ideal gas law to find the final temperature when the volume is doubled at constant pressure.