# Homework Help: Ideal gas theory

1. Jul 13, 2010

### Jenkz

1. The problem statement, all variables and given/known data

a) An ideal gas has a pressure of 1atm, volume of 0.5m^3m temperature of 300k. Find the number of moles.

b) Three moles of an ideal gas is at a pressure of 1x10^2 Nm^-2 and a temperature of 263K. Calculate the volume.

2. Relevant equations

1) PV = NRT
2) PV=NKbT

R = gas constant; Kb = Boltzman's constant

3. The attempt at a solution

I have found the answers to be a) 1.22x10^23moles and b) 65.6m^3.

What I don't understand, is when to use which equation. Why can I not use equation 1) for question a) vice versa.

Thanks.

2. Jul 13, 2010

### dulrich

Answer (a) is wrong. In PV = nRT, the "n" stands for moles. In PV = NkT, the "N" stands for number of molecules. There are 6.022 x 1023 molecules in a mole.

3. Jul 13, 2010

### Jenkz

Sorry that was meant to be 1.22x10^25 molecules.

Thank you for explaining.

4. Jul 13, 2010

### dulrich

Okay. I didn't check your math, but aren't you asked for the number of moles, rather than the number of molecules?

5. Jul 13, 2010

### Jenkz

Woops I was meant to write molecules instead of moles for question a) in my first post.

Must remember to re-read my posts before submitting them. Sorry about that!