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Chapter 14 Chemical Kinetics 293 expression, we get Rate = Because Cl is an intermediate, its concentration cannot appear in the rate law. Using the fast equilibrium in the first step, we see that = or = Substituting this expression into the last first rate expression, we get Rate = = Simplifying this expression, we see that Rate = k 14.119 For the elementary reaction 2NO(g) + we see that k₁ = For each mole of NOCI that reacts, 1 mole of NO and 0.5 mole of Cl₂ are generated. Because before any reaction only is present, [NO] = Substituting this into the first expression, we get = = Rearranging and substituting the specific values into this expression, we get = 0.0084 Cl₂ and = 2[NO] = 2 = = NO Conceptual Problems 14.121 Reactant concentrations drop more quickly for first-order reactions than for second-order reactions, so reaction A must be second-order. A plot of 1/[A] versus time will be linear Reaction B is first-order. A plot of versus time will be linear = Questions for Group Work 14.123 It is very tempting to think that the same descriptor that relates the concentration change to the rate change is the order of the reaction. This statement is incorrect because the reaction order is first order. For a first-order reaction, Rate = doubling the concentration of A doubles the reaction rate. For a second-order reaction, Rate = so doubling the concentration of A quadruples the reaction rate = Data Interpretation and Analysis 14.125 (a) The degradation of color of the preserves 5 follows first-order kinetics. A plot of In 4.5 (% Initial Color) versus Time yields a 4 straight line. In(% Initial Color) 3.5 3 2.5 2 1.5 0 50 100 150 200 Time (Days) (c) Yes, according to the data in Tables b-d, the color is maintained longer at cold temperature compared to warm temperature. At 200 days, the % of Initial Color is 52.62%, 14.06%, and 2.52% at 5.0 °C, 25.0 °C, and 40.0 °C, respectively. Copyright © 2017 Pearson Education, Inc.