# Homework Help: Gas Equilibria

1. Feb 5, 2009

### cantgetno

1. The problem statement, all variables and given/known data
The Equilibrium constant for A(g) -> 2B(g)
is 1x10^-2 at 1000k. Calculate the fraction on A which is dissociated at 1000k if the total pressure is
1 atm
10^-3 atm

2. Relevant equations
PV=nRT
B^2 / A = Ke (1x10^-2)

3. The attempt at a solution
for A PV=1x8.714x1000 = 8.714x10^3
for B PV=2x8.714x1000 = 17.428

All i can work out from this is that theres gunna be a 1:2 ratio? Im completely lost and my minds gone blank. Thanks in advance for the help

2. Feb 5, 2009

### Staff: Mentor

Solve in terms of partial pressures. What is sum of pA and pB?

3. Feb 5, 2009

### cantgetno

surely it would be pA+2pB=1atm ?
and im not very sure how to solve in terms of partial pressures

would i have
kp= pB^2 / pA
so 0.01 = pB^2 / pA

I've tried using a simultaneous equation with pA+2pB=1
and just end up with rubbish

4. Feb 5, 2009

### Staff: Mentor

Why pA + 2 pB? Do you know definition of partial pressure?

5. Feb 5, 2009

### cantgetno

because there's 2 moles of it? i thought that was right, my bad.

pA+pB=1atm that right?
would i be right to use a simlt equ then?

6. Feb 5, 2009

2*yes.

7. Feb 5, 2009

### cantgetno

ok using the equations i end up with the quadratic:
pB^2 + 0.01pB-0.01=0 so pB=0.095atm
so pA=0.905atm
and i can work out for the other atm

thanks