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Reaction MechanismsKinetics In-Class Practice Problems

By Leslie Peters,2014-05-09 22:01
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Reaction MechanismsKinetics In-Class Practice Problems

    Reaction Mechanisms/Kinetics In-Class Practice Problems

1. Nitrogen pentoxide reacts with nitric oxide in the gas phase according to the

    stoichiometric equation

    NO;NO3NO 252

    The following mechanism has been proposed.

    k1NO,?NO;NO 2523k-1

    k2NO;NO,?2NO 32

    (a) Assume that the steady-state approximation can be applied to NO and derive an 3

    equation for the rate of production of NO. 2

(b) How does the rate of production of NO relate to the rate of consumption of NO? 225

    2. A. Lindemann (Trans Faraday Soc., 17, 598(1922)) proposed the following mechanism for a unimolecular gas reaction

    k1 A;A,?A*;Ak-1

    k2 A*,?Y;Z

    The species A* is an enegized molecule that is present in low concentrations.

    (a) Apply the steady-state approximation to A* and obtain an expression for the rate

    (i.e., d[Y]/dt or d[Z]/dt) in terms of [A], k, k, and k. 1-12

    (b) Identify the conditions under which the rate is first order and those under which it

    is second order, and give expressions for the observed first and second order rate

    constants in terms of k, k and k. 1-12

    3. The rate law for the reaction of para-hydrogen to ortho-hydrogen

    kobsparaH(g),?orthoH(g) 22

     is

    d[orthoH]3/22 k[paraH]obs2dt

    Show that the following mechanism is consistent with this rate law and express k in obs

    terms of the rate constants for the individual steps of the reaction mechanism.

    k1paraH(g),?2H(g) fast equilibrium 2k-1

    keH(g);paraH,?orthoH(g);H(g) 22

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