Problem Sets 5 and 6 CHM 2046 Spring 2013 Chapter 15 Kinetics Here is Problem set 5 1 Nitric oxide reacts with bromine gas at elevated temperatures according to the equation 2 NO g Br2 g 2 NOBr g The experimental rate law is rate k NO Br2 In a certain reaction mixture the rate of formation of NOBr g was found to be 4 50 x 10 4 mol L l s l What is the rate of consumption of Br2 g also in mol L l s l a 4 50 x 10 4 mol L l s l b 2 25 X 10 4 mol L l s l c 9 00 X 10 4 mol L l s l d 2 12 x 10 4 mol L l s l e 2 03 x 10 3 mol L l s l 2 A reaction has a rate law rate k A B 2 What is the overall order of the reaction a 2 b 3 c 0 d 1 e 4 3 For the reaction 2 XO O2 2 X02 some data obtained from measurement of the initial rate of reaction at varying concentrations are given below run XO O2 1 0 010 0 010 2 0 010 0 020 3 0 030 0 020 rate mol L l s l 2 5 5 0 45 0 The rate law is therefore a rate k XO 2 O2 d rate k XO 2 O2 2 b rate k XO O2 2 e rate k XO 2 O2 2 c rate k XO O2 4 Given this data in a study on how the rate of a reaction was affected by the concentration of the reactants RUN 1 2 3 4 5 A M 0 200 0 200 0 600 0 200 0 200 B M 0 100 0 400 0 100 0 100 0 200 C M 0 600 0 400 0 200 0 200 0 400 The rate constant for this reaction all in the same units is a 6667 b 208 c 2083 d 139 e 2500 Initial Rate mol L 1 s 1 5 00 80 0 15 0 5 00 20 0 5 The units of a rate constant for zero first and second order reactions are given in the textbook If the time units are minutes what would you expect the units to be for a third order reaction a 1 min3 b mol2 L2 min c L mol min2 d L2 mol2 min e L2 mol2 min2 6 The decomposition of an aldehyde solution in carbon tetrachloride is a first order reaction with a rate constant of 1 20 x 10 3 min l If we start with aldehyde 0 0500 molar what will the concentration be 150 minutes later a 0 00900 M b 0 0418 M c 0 00926 M d 0 00499 M e 0 000333 M 7 For the reaction A B C the rate law is k A If it takes 80 0 seconds for 70 0 of a 10 0 gram sample of A to be transformed into products what is the value of the rate constant a 0 00450 s 1 b 0 0290 s 1 c 0 00530 s 1 d 0 0150 s 1 e 5 40 s 1 8 The half life of a reaction was found to be inversely dependent on the concentration of the starting material Thus we can say that a the reaction is zero order b the reaction is first order c the reaction is second order d the reaction starts out first order and changes to second order after one half life e the reaction starts out second order and changes to first order after one half life 9 The initial concentration of a reactant in a first order reaction is 0 620 molar What will be its concentration after 3 half lives a 0 0388 M b 0 310 M c 0 0775 M d 0 155 M e 4 96 M 10 The reaction A B C products has a rate law rate k A C 2 Which of the following will result in an increase in the rate constant for the reaction 1 increasing the temperature 2 adding a catalyst 3 doubling the concentration of reactant C a only one of these only 1 or only 2 or only 3 b 1 and 2 only c 1 and 3 only d 2 and 3 only e all three will result in an increase in the rate constant for the reaction ANSWERS TO SET 5 1 B 2 B 3 A 4 E 5 D 6 B 7 D 8 C 9 C 10 B Here is Problem set 6 1 A particular reaction has an activation energy of 51 6 kJ mol rxn How much faster is the reaction at 50 oC versus 25 oC a 2 times b 5 times c 3 times d half as fast d 20 as fast 2 For a one step reaction the activation energy for the forward reaction is 40 0 kJ mol and the enthalpy of reaction is 20 0 kJ mol Which statement below is true a The activation energy of the forward reaction would be affected to a greater extent than the activation energy of the reverse reaction by addition of a catalyst b The value for the enthalpy of reaction would be decreased by addition of a catalyst c The reaction is endothermic d The reverse reaction is slower than the forward reaction smaller rate constant e The reaction rate would be decreased by an increase in temperature 3 For a certain chemical reaction the rate constant at 250 0 C is 0 00383 s 1 and the activation energy is 22 40 kilojoules Calculate the value of the rate constant at 335 0 C a 0 00513 s 1 b 0 00946 s 1 c 0 00787 s 1 d 0 0224 s 1 e 0 000640 s 1 4 For a particular chemical reaction the rate constant at 30 0 C is 1 38 X 10 4 L mol 1 s 1 while the value at 49 0 C is 1 21 X 10 3 L mol 1 s 1 What is the activation energy for this reaction a 92 8 kJ b 200 kJ c 40 4 kJ d 343 kJ e 56 4 kJ 5 The reaction A 3 B D F was studied and the following mechanism was finally determined A B C fast C B D E slow E B F very fast The step with largest activation energy is a the first step b the second step c the third step d none of the steps has an activation energy e all of the steps have the same activation energy 6 The decomposition of hydrogen peroxide in solution and in the presence of iodide ion was studied in laboratory and the following mechanism proposed based on the experimental data H2O2 I H2O IO slow H2O2 IO H2O O2 I fast Which one of the following statements is false Choose answer E if more than …