Gas Equilibria

  • Thread starter cantgetno
  • Start date
  • #1
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Homework Statement


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

Homework Equations


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

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
 

Answers and Replies

  • #2
Borek
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Solve in terms of partial pressures. What is sum of pA and pB?
 
  • #3
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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
Borek
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2,871
Why pA + 2 pB? Do you know definition of partial pressure?
 
  • #5
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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
Borek
Mentor
28,473
2,871
2*yes.
 
  • #7
23
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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
 

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