# Homework Help: Internal Energy of argon

1. Apr 23, 2013

### kingstar

1. The problem statement, all variables and given/known data
Argon is a monatomic gas for which all the internal energy of the molecules may be considered to
be translational kinetic energy.
Molar mass of argon = 4.0 x 10-2
kg.
The Boltzmann constant = 1.38 x 10-23 J kg-1
.
The Avogadro constant = 6.02 x 1023 mol-1
.
Calculate the internal energy of 8.0 g of argon gas at a temperature of 100 K.

2. Relevant equations

pV=nRT or pV=NKT

U=3/2NKT

3. The attempt at a solution
So far I'm assuming you need U=3/2NKT

We know that 1 mol = 4x10^-2 Kg

So i did 0.008/4x10^2 = 0.2

0.2 x Avagardo's Constant = 1.204x10^23

And subbed that into U=3/2NKT as N

The final answer I got was as U was 248.4J

To be honest i have no clue what I did as its been so long since I've done Physics.

Thanks for any help or any pointers in the right direction.

2. Apr 23, 2013

### Staff: Mentor

That looks correct. By the way, since you calculated the amount of argon in moles, you could've used U=3/2nRT instead of calculating N, but the result is the same.