(i) Consider the following equilibrium reaction.
    2SO2(g) + O2(g) <-----> 2SO3(g)     ∆H = –198 kJ
    Using Le Chatelier’s Principle, state and explain what will happen to
    the position of equilibrium if
    (a)    the temperature increases.
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    (b)    the pressure increases.
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Ans : (a)    (position of) equilibrium shifts to the left/towards reactants;
                (forward) reaction is exothermic/∆H is negative/the reverse
                reaction is endothermic/OWTTE;   
                Do not accept “Le Chatelier’s Principle” without some additional
                explanation.
        (b)    (position of) equilibrium shifts to the right/towards products;
                fewer gas molecules on the right hand side/volume decreases in
                forward reaction/OWTTE;    
                Do not accept “Le Chatelier’s Principle” without some additional
                explanation.


(ii)    The equilibrium between nitrogen dioxide (dark brown) and dinitrogen
        tetroxide (colourless) is represented by the following equation.
        2NO2(g) <---->  N2O4(g)        ∆H = negative Kc = 1 at 328K
        (a)    Write the equilibrium constant expression, Kc.
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        (b)    State and explain the effect of an increase in temperature on
                the value of Kc.
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        (c)    State and explain the visible change that takes place as a
                result of a decrease in pressure, after equilibrium is
                re-established.
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        (d)    Two moles of NO2(g) and two moles of N2O4(g) were placed in an
                empty 1 dm3 container and allowed to come to equilibrium at
                328 K.
                Predict, with reference to the value of Kc, whether the
                equilibrium mixture would contain more or less than two moles of
                NO2(g).
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Ans : No ECF throughout this question.
        (a)     1
        (b)     Kc decreases;
                forward reaction is exothermic/∆H is negative/equilibrium
                moves to left/OWTTE;    2
        (c)    (mixture will get) darker/darker than expected;
                equilibrium position moves to the left/towards reactants as
                there is an increase in the number of moles of gas from
                right to left; 
        (d)    (equilibrium mixture contains) less (than 2 moles NO2);
                given values make   i.e. too much NO2/OWTTE;