3.1Chapter 14 Chemical Kinetics (1 per page)

3.1Chapter 14 Chemical Kinetics (1 per page) - Chemical...

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Chemical Kinetics: Ch. 14 14-1 The Rate of a Chemical Reaction 14-2 Measuring Reaction Rates 14-3 Effect of Concentration on Reaction Rates: The Rate Law 14-4 Zero-Order Reactions 14-5 First-Order Reactions 14-6 Second-Order Reactions 14-7 Reaction Kinetics: A Summary
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Chemical Kinetics 14-8 Theoretical Models for Chemical Kinetics 14-9 The Effect of Temperature on Rates 14-10 Reaction Mechanisms 14-11 Catalysis
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• Concerned with the speed (or rate) at which chemical reactions take place and the mechanisms by which they occur. •A reaction mechanism is the step by step sequence of chemical events by which reactant molecules are turned into product molecules. • The rate at which a reaction proceeds depends on the mechanism, so by measuring rates we can hope to better understand mechanisms! What is Chemical Kinetics?
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14-1 The Rate of a Chemical Reaction • Rate of change of concentration with respect to time. 2 Fe 3+ (aq) + Sn 2+ (aq) 2 Fe 2+ (aq) + Sn 4+ (aq) t = 38.5 s [Fe 2+ ] = 0.0010 M Δ t = 38.5 s Δ [Fe 2+ ] = (0.0010 – 0) M Average Rate of Fe 2+ Formation Δ [Fe 2+ ] Δ t 0.0010 M 38.5 s 2.6 × 10-5 M s -1 = = =
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Rates of Chemical Reactions Δ [Sn 4+ ] Δ t 2 Fe 3+ (aq) + Sn 2+ (aq) 2 Fe 2+ (aq) + Sn 4+ (aq) Δ [Fe 2+ ] Δ t = 1 2 Δ [Fe 3+ ] Δ t = - 1 2 Rate of disappearance is a negative quantity Rate of formation is a positive quantity What number should we take for the rate??
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General Rate of Reaction a A + b B c C + d D Rate of reaction = -rate of disappearance/consumption of reactants = Δ [C] Δ t 1 c = Δ [D] Δ t 1 d Δ [A] Δ t 1 a = - Δ [B] Δ t 1 b = - = rate of appearance/production of products
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14-2 Measuring Reaction Rates H 2 O 2 (aq) H 2 O(l) + ½ O 2 (g) 2 MnO 4 - (aq) + 5 H 2 O 2 (aq) + 6 H + 2 Mn 2+ +8 H 2 O(l) + 5 O 2 (g) A very simple device for measuring the rate of a reaction that produces gas
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H 2 O 2 (aq) H 2 O(l) + ½ O 2 (g) -(-1.7 M / 2800 s) = 6 × 10 -4 M s -1 -(-2.32 M / 1360 s) = 1.7 × 10 -3 M s -1 Rate = - Δ [H 2 O 2 ] Δ t Determining and Using an Initial Rate of Reaction.
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14-3 Effect of Concentration on Reaction Rates: The Rate Law a A + b B …. g G + h H …. Rate of reaction = k [A] m [B] n …. Rate constant = k Overall order of reaction = m + n + …. In general, m a and n b! With the rate law determined, we can calculate the rate for known concentrations and derive an equation for concentration as a function of time!
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Method of Initial Rates • A method that can be used to determine the rate law for a reaction • Requires that the initial rate be determined: At this stage the concentration of the reactants is known (i.e. under our control)
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Method of Initial Rates: Example
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14-4 Zero-Order Reactions A products R rxn = k [A] 0 R rxn = k [ k ] = mol L -1 s -1 0 [] f A k t =
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This note was uploaded on 04/04/2011 for the course SCIENCE CHEM 120 taught by Professor Fenster during the Winter '11 term at McGill.

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3.1Chapter 14 Chemical Kinetics (1 per page) - Chemical...

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