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Homework Help: Halved volume with chemical equilibrium

  1. Nov 11, 2012 #1
    1. The problem statement, all variables and given/known data
    The reaction is PCl5 (g) <=> PCl3 (g) + Cl2
    In an unknow volume, the following mixture is balanced:
    0.14 atm of PCl5
    0.36 atm of PCl3
    0.50 atm of Cl2

    What would be the the pressure of the whole mixture if the volume would be halved?

    (the answer is 1.88 atm)

    2. Relevant equations
    p1+p2+p3=1 atm

    3. The attempt at a solution
    Since the answer is 1.88 atm I assumed the ideal gas laws aren't valid in this question because then the pressure would be 2 atm. I calculated Kp and it's 1.29 atm. But now I'm stuck.
  2. jcsd
  3. Nov 11, 2012 #2


    User Avatar
    Gold Member

    1. If the ideal gas law isn't valid for this question, good luck then. Luckily, they are applicable. (Generally are, unless Van der waal's Gas is given.)

    2. Since the system is disturbed, the equilibrium will shift so as to minimize the effect. Since the volume is halved or the pressure is doubled, the equilibrium will shift to decrease the pressure (Guess how?) But it can only do it to some extent.

    Try gathering some relevant know-how on how to solve these types of problems (they are generally book illustrations).
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