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CAIE A Level Chemistry 9701 · Reaction kinetics

Reaction kinetics: describe question

Describe7 marksChallenge

Nitrogen monoxide and oxygen react to form nitrogen dioxide:

2 NO(g)+OX2(g)→2 NOX2(g)\ce{2NO(g) + O2(g) -> 2NO2(g)}

The following two-step mechanism is proposed for this reaction:

Step 1: NO(g)+NO(g)⇌NX2OX2(g)\ce{NO(g) + NO(g) <=> N2O2(g)} (fast, equilibrium established)

Step 2: NX2OX2(g)+OX2(g)→2 NOX2(g)\ce{N2O2(g) + O2(g) -> 2NO2(g)} (slow)

Describe:

(a) the rate-determining step of this reaction, (b) the intermediate in the mechanism, (c) the rate equation that is consistent with this mechanism, (d) the overall order of reaction, (e) how the rate constant, kk, changes if the temperature is increased, (f) why increasing the temperature affects the rate constant in the way you described, (g) why the proposed mechanism is consistent with the overall stoichiometric equation.

0 words · 7 marks

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7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.

Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.

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