# Homework Help: Gases help

1. Nov 8, 2006

### CathyLou

I'd really appreciate it if someone could please give me some hints over how to do the following questions as I'm currently really stuck.

8.

(a) What is the average velocity of the molecules in a gas?

9. Two moles of He gas are at a pressure of 105 Pa and have a volume of 0.5m3.

(a) What is the mean square speed of the He atoms?

(b) What is the root mean square speed of the He atoms?

10. What is the average kinetic energy of the particles of a gas at 400ºC?

Thank you.

Cathy

2. Nov 8, 2006

### Andrew Mason

Why not show us what your thoughts are first?

What does the speed of molecules in a gas depend on? How is the distribution of speeds in a gas expressed mathematically?

AM

3. Nov 8, 2006

### CathyLou

It is something to do with the mass of the gas and its volume or the pressure that it is under?

4. Nov 8, 2006

### CathyLou

I'm now okay with number 10 but am still stuck on the others.

Here is my working so far for 9a:

PV = (1 x 105) x 0.5

PV = 50000

PV = nRT

So 50000 = 2 x 8.31 x T

T = 3008ºK

½ m x average speed squared = 3/2 k T

k = 1.38 x 10-23

so ½ m x average speed squared = 6.23 x 10-20

I'd really appreciate it if someone could please tell me what I've done wrong.

Thank you.

Cathy

5. Nov 8, 2006

### Max Eilerson

Your method is correct but how does PV = 105 x 0.5 = 50000