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26. Reaction kinetics

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  1. 26.1 Rate equations, orders and rate constants

    1. • Explain and use the terms rate equation, order of reaction, overall order of reaction, rate constant, half-life, rate-determining step and intermediate

    2. • The initial rates method and half-life method - (a) understand and use rate equations of the form rate = k [A]m[B]n (for which m and n are 0, 1 or 2) - (b) deduce the order of a reaction from concentration–time graphs or from experimental data relating to - (c) interpret experimental data in graphical form, including concentration–time and rate–concentration graphs - (d) calculate an initial rate using concentration data - (e) construct a rate equation

    3. • (a) show understanding that the half-life of a first-order reaction is independent of concentration: (b) use the half-life of a first-order reaction in calculations

    4. • Calculate the numerical value of a rate constant, e.g. by: - (a) using the initial rates and the rate equation - (b) using the half-life, t - 2 - 1 , and the equation k = 0.693 / t - 2 - 1

    5. • For a multi-step reaction: - (a) suggest a reaction mechanism that is consistent with the rate equation and the equation for the overall reaction - (b) predict the order that would result from a given reaction mechanism and rate-determining step - (c) deduce a rate equation using a given reaction mechanism and rate-determining step for a given reaction - (d) identify an intermediate or catalyst from a given reaction mechanism - (e) identify the rate determining step from a rate equation and a given reaction mechanism

    6. • Describe qualitatively the effect of temperature change on the rate constant and hence the rate of a reaction

  2. 26.2 Homogeneous and heterogeneous catalysts

    1. 26.2.1Catalysts can be homogeneous or heterogeneous

      • Explain that catalysts can be homogeneous or heterogeneous

    2. 26.2.2Heterogeneous catalyst action

      • Describe the mode of action of a heterogeneous catalyst to include adsorption of reactants, bond weakening and desorption of products, e.g.: - (a) iron in the Haber process - (b) palladium, platinum and rhodium in the catalytic removal of oxides of nitrogen from the exhaust gases of car engines

    3. 26.2.3Mode of action of a homogeneous catalyst

      • Describe the mode of action of a homogeneous catalyst by being used in one step and reformed in a later step, e.g.:: (a) atmospheric oxides of nitrogen in the oxidation of atmospheric sulfur dioxide; (b) Fe 2+ or Fe3+ in the I–/S2O8; 2– reaction