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A2 Chemistry: Calculating concentration given Kc question help Watch

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    I'm having a terrible time with this question. The answer is 0.897 mol dm–3 but I'm stuck at getting 0.93 for some reason. Our teacher told us that she is giving the same type of question in our test tomorrow so I am absolutely terrified. Here it is:

    Phosphorus pentachloride decomposes as shown:
    PCl5 (g) -----> PCl3 (g) + Cl2 (g)
    Given that the equilibrium constant for this reaction is 11.5 mol dm-3 at 300 K, what is the equilibrium concentration of PCl3 when the concentration of PCl5 at equilibrium is 0.07 mol dm-3

    Ideas? Any help would be appreciated
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    11.5=[Cl2] * [PCl3]/0.07

    let [PCl3] = x

    11.5* 0.07 = x^2

    x = sqrt (11.5* 0.07)

    x = 0.897 mol/dm3
 
 
 
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