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    "2 moles of X was heated to a temperature of 2000°C until equilibrium was established under a total pressure of 8 x 10^7 Nm^-2. At equilibrium, X was found tohave undergone 20% dissociation. Calculate Kp.
    X(g) +Y(g) + 2 Z(g)"
    I have attempted this question but I think I may have gotten the calculating the moles at equilibrium part incorrect because the 20% dissociation confused me a bit.
    Can anyone explain how I could do this correctly? Much appreciated.
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    Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.

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    (Original post by CryingWaffle)
    "2 moles of X was heated to a temperature of 2000°C until equilibrium was established under a total pressure of 8 x 10^7 Nm^-2. At equilibrium, X was found tohave undergone 20% dissociation. Calculate Kp.
    X(g) +Y(g) + 2 Z(g)"
    I have attempted this question but I think I may have gotten the calculating the moles at equilibrium part incorrect because the 20% dissociation confused me a bit.
    Can anyone explain how I could do this correctly? Much appreciated.
    The term dissociation suggests that one compound has broken apart. This is not reflected by the equation given. I will show you a method based on:

    X(g) <==> Y(g) + 2Z(g)

    20% dissociation simply means that 20/100 of the original sample has decomposed (dissociated) at that temperature.

    You are told that you start with 2 moles therefore 2 x 20/100 moles have dissociated = 0.4 moles

    So at equilibrium you have a mole ratio of:

    X = 2.0 - 0.4 = 1.6 mol
    Y = 1 x 0.4 = 0.4 mol
    Z = 2 x 0.4 = 0.8 mol

    Gas partial pressure = total pressure x mol fraction

    Mol fractions:

    X= 1.6/2.8 = 0.571
    Y = 0.4/2.8 = 0.143
    Z = 0.8/2.8 = 0.286

    Partial pressures:

    X = 0.571 x 8 x 107 = 4.57 x 107
    Y = 0.143 x 8 x 107 = 1.14 x 107
    Z = 0.286 x 8 x 107 = 2.29 x 107

    now substitute values into kp = p(Y) x p(Z)2/p(X)

    kp = 1.30 x 1014
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    Thanks a lot for your help!
 
 
 
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