# Energies of gas particles

1. Aug 23, 2008

### DanAbnormal

Just a quickie.

For example, the total kinetic energy of N molecules is

= (3/2)NkT = (3/2)nRT

If a question were to ask you to find the such energy for a sample of N$$_{2}$$ would it make the equation

(5/2)kT?

Does the subscript 2 make it diatomic, and hence have two molecules, im not sure, it could cost me marks though.

2. Aug 23, 2008

### Astronuc

Staff Emeritus
3. Aug 23, 2008

### DanAbnormal

Sorry, "N" isnt the number of molecules. Its supposed to be N subscript 2, as in "N" for Nitrogen.
Does the subscript 2 make the N from the equation = 2?

4. Aug 23, 2008

### Renge Ishyo

N2 is one molecule composed of two nitrogen atoms connected by a triple bond. You wouldn't have to modify your original equation to do the calculation as far as I can see.

5. Aug 23, 2008

### Ygggdrasil

N2 is one molecule that consists of two atoms. The average translational kinetic energy of any gas will be (3/2)NkBT.

You may be confusing the average kinetic energy with the heat capacity as the molar heat capacity (Cv). Cv for a diatomic gas is (5/2)kBT, whereas Cv for a monatomic gas is (3/2)kBT. The difference comes because diatomic molecule have rotational modes of motion which can absorb energy whereas monatomic atoms do not. However, the rotation of diatomic molecules does not affect their translational kinetic energy.

Last edited: Aug 23, 2008