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Reaction Mechanisms

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The reaction of a hyrogrn halide A with an olefin B to give product P according to the stoichiometric relationship:

A + B -> P

is proposed to occur by the following mechanism:

2A <-> A2 (fast to equilibrium)

A + B <-> C (fast to equilibrium)

A2 + C -> P + 2A (slow)

(a) Based on this mechanism, derive an expression for the velocity (rate) of the reaction of the concentration of only reactants and stable product.

(b) In a particular ecperiment, equal concentrations of A and B are mixed together, and both the inital rate vo and the half-life t 1/2 are determined. Based on your answer to part (a), predict for a subsequent experiment:

(i) The effect on vo if the initial concentrations of both A and B are doubled.

(ii) The effect on t 1/2 if the initial concentrations of both A and B are doubled.

(iii) The effect on vo if the initial concentration of A id unchanged and the initial concentration of B is increased tenfold.

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Solution Preview

The whole reaction can be written as:
2A + A + B <-> A2 + C -> P + 2A
or, 3A + B <-> (A2C) -> P + 2A

Therefore,
d[P]/dt = k2*[(A2C)]

For steady state:
d[A2C]/dt = k1*[A]^3*[B] - k1'*[(A2C)] - k2*[(A2C)] = 0
=> [A2C] = k1*[A]^3*[B]/{k1'+k2}

Therefore,
d[P]/dt = k2*k1*[A]^3*[B]/k3 ...

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