# Homework Help: Monatomic and diatomic mix

1. May 31, 2007

### skinard360

n_1 moles of a monatomic gas and n_2 moles of a diatomic gas are mixed together in a container.
Derive an expression for the molar specific heat at constant volume of the mixture.

c sub v = 3/2 R for a monatomic gas
5/2 R for a diatomic gas

thermal energy for a monatomic gas = 3/2 NkT = 3/2 nRT
diatomic Eth = 5/2 NkT = 5/2 nRT

c = J/molK, R = J/molK, n = mol

I started off by looking at the units and figuring that I needed to divide the n's somehow and multiply that times R...but I have tried many equations and can't seem to find one that works, and I can't figure out logically how that would work out...does anyone have any ideas?? I'm desperate

2. May 31, 2007

### mukundpa

If the temperature of the mixture is to be raised by dT the heat required (at constant volume) will be

n1(3R/2)*dT + n2(5R/2)*dT

Now what is the definition of molar specific heat?

3. May 31, 2007

### skinard360

I figured it out, thank you!