# Change in internal engergy of a monatomic ideal gas

1. Nov 17, 2009

### alexthelion

1. The problem statement, all variables and given/known data
A monatomic ideal gas expands from 1.00 meters cubed to 2.50 meters cubed at a constant pressure of 2.00 x 10^5 Pa. Find the change in the internal energy of the gas.

2. Relevant equations

$$\Delta$$U = Q + W

3. The attempt at a solution

Well, I know how to find work, which is -P$$\Delta$$V

But I'm having trouble finding the energy transferred into the system by heat, or Q, because the problem does not give a specific value for it.

I would much appreciate it if someone could give me some pointers as to how to find Q.

2. Nov 17, 2009

### kuruman

How is Q related the the specific heat at constant pressure?

3. Nov 17, 2009

### alexthelion

I don't exactly know, I do know that $$\Delta$$U = 3/2nR$$\Delta$$T for a monatomic gas, where the molar specific heat is given by Cv = 3/2R

4. Nov 17, 2009

### kuruman

If you know CV, then Cp = CV + R. Also at constant pressure Q = n CpΔT. Now you can put it together.

5. Nov 18, 2009

### alexthelion

Aha, thanks for the help! I got it.