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Chemistry Equilibria Help

  1. Jul 17, 2012 #1
    Hey guys, I've just got an assessment coming up. I just want to double check if I got it right and perhaps people can help me with a question or two.

    1. Consider the reaction A(s) + 3B(g) = 4C(g), ΔH°=-16.6kJ

    i) Given Kc = 0.00570, calculate Kp at 198°C.
    ii) Given p(B) = 0.10atm and p(C) = 0.90 atm calculate the reaction quotient, Qp, and determine in what direction the reaction will proceed.
    iii) If, after the reaction reaches equilibrium, the temperature of the system increased, in what direction will the reaction proceed.
    iv) If, after the reaction reaches equilibrium, the pressure of the system increased, in what direction will the reaction proceed.

    A(s) + 3B(g) = 4C(g)
    kp = kc (RT)n

    kp = x
    kc = 0.00570
    R = 0.0821 atm
    T = 198+273 = 471K
    n = 1

    kp = 0.00570 (0.0821 x 471)1
    = 0.22041 atm
    = 0.22 atm (2 dp)

    Do I have to include the number of moles in the solid or not? So in that case, the n = 0. But it doesn't make much sense having kp=kc right?

    ii) solids not included.
    ∴ [C]4 / 3
    Qp = 0.9^4 / 0.1^3
    = 0.6561 / 0.001
    = 656.1

    Reaction would go forwards?
    iii) Forward
    iv) Forward

    I honestly don't really understand the concept of which way the reaction is gonna go. If someone could explain it it'd be great.

    Thanks in advance.
  2. jcsd
  3. Jul 20, 2012 #2
  4. Jul 21, 2012 #3


    User Avatar

    no you dont have to include no.of moles of solid.

    no, it would go backwards,as Qp>Kp.
    for (iii) and (iv) read le chatelier's principle.

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