General Chemistry by Whitten, Atwood, Morrison Chapter 16 solutions

General Chemistry by Whitten, Atwood, Morrison Chapter 16 solutions

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167 Chemical Kinetics 16 16-1 Nature of reactants : Chemical identities of reactants affect the rates of possible reactions. Factors such as particle size of solid reactants or efficiency of mixing of components in solution also influence reaction rates because they affect the ability of the reacting particles to encounter one another. Physical states of elements that occur as allotropes can affect rates because the atoms are bonded differently in various forms of the same element. Reactions of ions in solution are often more rapid than those that require breaking of covalent bonds. Concentrations of reactants : Higher reactant concentrations increase the likelihood of the reactant species colliding to allow reaction; reaction rate increases. Temperature : At higher temperatures, the collisions between reactant species are both more frequent and more energetic so that a greater number of sufficiently energetic collisions occur per unit time; reaction rate increases. Presence of a catalyst : A catalyst alters (nearly always decreases) the minimum energy necessary for the reaction to occur by providing an alternate pathway for the reaction; reaction rate is changed (nearly always increased). 16-3 A rate-law expression indicates the dependence of reaction rate on the concentrations of reactants. For example, for a reaction in which A and B are reactants, the rate-law expression is of the general form Rate = k [A] x [B] y where k is the specific rate constant, and the molar concentrations of reactants are each raised to some power. These exponents are not necessarily related to the coefficients in the balanced overall chemical equation and must be determined experimentally. To do this, we measure the reaction rate for various combinations of reactant concentrations; then we analyze the results to deduce the values of the exponents. One such method of analysis is the method of initial rates (Section 16-3, Examples 16-3 and 16-4). 16-5 The mechanism of the overall reaction is the sequence of steps by which the reactants are converted into products. A reaction can never occur faster than its slowest step. The order of a reaction is a description of the exponents to which the reactant concentrations appear in the experimentally determined rate-law expression. For instance, a reaction for which the rate-law expression is Rate = k [A] x [B] y is said to be x th order in reactant A, y th order in reactant B, and ( x + y ) th order overall. The values of x and y are related to the coefficients of the reactants as indicated by the slowest step of the mechanism, influenced in some cases by earlier steps. 16-7 (a) Rate of rxn = Δ [H 2 O 2 ] Δ t = Δ [H + ] 2 Δ t = Δ [I ] 2 Δ t = Δ [I 2 ] Δ t = Δ [H 2 O] 2 Δ t (b) Rate of rxn = Δ [NO] 2 Δ t = – Δ [Br 2 ] Δ t = Δ [NOBr] 2 Δ t
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168 (c) Rate of rxn = Δ [CH 3 COOH] Δ t = Δ [OH ] Δ t = Δ [CH 3 COO ] Δ t = Δ [H 2 O] Δ t (d) Rate of rxn = Δ [N 2 O 5 ] Δ t
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General Chemistry by Whitten, Atwood, Morrison Chapter 16 solutions

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