Practice Problems Test 2 1 Write the reaction rate expressions for the following reactions in terms of the disappearance of the reactants and the appearance of products a 2H2 g O2 g 2H2O g b 4NH3 g 5O2 g 4NO g 6H2O g 2 Consider the reaction N2 g 3H2 g 2NH3 g Suppose that at a particular moment during the reaction molecular hydrogen is reacting at the rate of 0 074 M s a At what rate is ammonia being formed b At what rate is molecular nitrogen reacting 3 Consider the reaction X Y Z From the following data obtained at 360 K a Determine the order of the reaction 0 30 M and that of Y is 0 40 M b Determine the initial rate of disappearance of X when the concentration of X is Initial Rate of Disappearance X M s X M Y M 0 053 0 127 1 02 0 254 0 509 0 10 0 20 0 40 0 20 0 40 0 50 0 30 0 60 0 60 0 30 4 Consider the reaction A B The rate of the reaction is 1 6 X 10 2 M s when the concentration of A is 0 35 M Calculate the rate constant if the reaction is a First order in A and b Second order in A 5 The thermal decomposition of phosphine PH3 into phosphorus and molecular hydrogen is a first order reaction 4Ph3 g P4 g 6H2 g The half life of the reaction is 35 0 s at 680 degrees C Calculate a The first order rate constant for the reaction b The time required for 95 percent of the phosphine to decompose 6 The rate constant for the second order reaction 2NO2 g 2NO g O2 g is 0 54 M s at 300 degrees C How long in seconds would it take for the concentration of NO2 to decrease from 0 62 M to 0 28 M 7 Given the same reactant concentrations the reaction CO g Cl2 g COCl2 g at 250 degrees C is 1 50 X 10 3 times as fast as the same reaction at 150 C Calculate the activation energy for this reaction Assume that the frequency factor is constant 8 The rate constant of a first order reaction is 4 60 X 10 4 s 1 at 350 C If the activation energy is 104 kJ mol calculate the temperature at which its rate constant is 8 80 X 10 4 s 1 9 Consider the first order reaction CH3NC g CH3CN g Given that the frequency factor and activation energy for the reaction are 3 98 X 10 13 s 1 and 161 kJ mol respectively calculate the rate constant at 600 degrees C 10 The rate at which tree crickets chirp is 2 0 X 10 2 per minute at 27 degrees C but only 39 6 per minute at 5 degrees C From these data calculate the activation energy for the chirping process Hint the ratio of rates is equal to the ratio of rate constants 11 The reaction 2A 3B C is first order with respect to A and B When the initial concentrations are A 1 6 X 10 2 M and B 2 4 X 10 3 M the rate is 4 1 X 10 4 M s Calculate the rate constant of the reaction 12 What are the units of the rate constant for a third order reaction 13 The thermal decomposition of N2O5 obeys first order kinetics At 45 C a plot of ln N2O5 versus t gives a slope of 6 18 X 10 4 min 1 What is the half life of the reaction 14 Consider the following elementary step X 2Y XY2 a Write a rate law for this reaction b If the initial rate of formation of XY2 is 3 8 X 10 3 M s and the initial concentrations of X and Y are 0 26 M and 0 88 M what is the rate constant of the reaction 15 The activation energy Ea for the reaction 2N2O g 2N2 g O2 g delta H 164 kJ mol is 240 kJ mol What is the Ea for the reverse reaction Answers 1 a rate 1 2 delta H2 delta t delta O2 delta t 1 2 delta H2O delta t b rate 1 4 delta NH3 delta t 1 5 delta O2 delta t 1 4 delta NO delta t 1 6 delta H2O delta t 2 a 0 049 M s b 0 025 M s 3 X 4 X 5 X a Third Order b 0 38 M s a 0 046 s 1 b 0 13 M s a 0 0198 s 1 b 151 s 6 3 6 s 7 135 kJ mol 8 644 K 9 9 25 X 10 3 s 1 10 51 0 kJ mol 11 10 7 M s 12 M 2 s 1 13 1 12 X 10 3 min 14 X a Rate k X Y 2 b 1 9 X 10 2 M 2 s 15 404 kJ mol
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