# Homework Help: Piston Problem

1. Aug 28, 2007

### mojo4king

Hello,
Piston question,i need to work out the time when no molecules are left in the gaseous system..
I have worked out the relative velocity..if i multiply that by the mean free path to get
the diffusion coefficient am i getting any closer to the answer?
I can work out the change in time using an equation involving collision frequency but i'm
guessing mean free path has to be involved somewhere..
This question had been bugging me for weeks!!
Regards.

2. Aug 28, 2007

### chemisttree

I've only just seen it and its already bugging me! Could you be more specific? Why is it a piston problem and not a diffusion problem?

3. Aug 28, 2007

### mojo4king

closed system,frictionless piston initially filled with gas molecules A, piston mass 100g,area 10cm2,10cm from bottom,pressure outside 1atm,temp. iniside system 900oC, i have already calculated the initial number of moles using pv=nrt...

Next using the collision flux multiplied by the area i have determined the initial rate.

Final question is how would i calculate the time after which no molecules of A will remain in the gaseous phase in the system (doesn't require complex integration).

Many thanks.

4. Aug 29, 2007

### Gokul43201

Staff Emeritus
Please quote the original question verbatim.