# Finding the exerting forces in a container

1. Jun 3, 2012

### Philip Wong

1. The problem statement, all variables and given/known data
A sealed cubical container 20.0 cm on a side contains three times Avogadro’s number of molecules at a temperature of 20.0°C. Find the force exerted by the gas on one of the walls of the container.

2. Relevant equations
$PV=nRT$
$P=F/A$

3. The attempt at a solution
Hello people, here is what I understands from the question

$V=(0.2)^3$
$PV=3*n*R*(20+273K)$
$P*(0.2)^3=3*n*8.31*(293)$
$P=(7304.49n)/(0.2)^3$
$P=913061.25n$

This is where I don't understands, according to the answer shown by the lecturer, he uses n=3 instead of 3n (which is what I've suggested). Can someone show me why is this?

thanks,
Phil

2. Jun 3, 2012

### Infinitum

Hi Phil!

The question has given you that the number of molecules in the container is three times the Avogadro number, and one mole is equivalent to Avogadro's number of molecules. So, how many moles totally?

3. Jun 4, 2012

### Philip Wong

oh right. got it.

thanks!