Chapter 14 Lecture on chemical kinetics

21. For the reaction: A  2 B , which of the following is a correct expression for the reaction rate? t   Rate [A] = t   Rate 2 [A] = 2. t   Rate 2 [B] = 3. 4. t   Rate 2 [B] = 1.

22. Correct Answer: In general for aA + bB  cC + dD t   Rate [A] = t   Rate 2 [A] = 2. t   Rate 2 [B] = 3. 4. t   Rate 2 [B] = 1. =  =  = =

30. For the reaction: A + 2 B  B 2 A Doubling [A] doubles the rate of the reaction. However, doubling [B] increases the rate 4  . What is the correct rate law expression? [A][B] Rate k = 3. 2. 4. 1.

31. For the reaction: A + 2 B  B 2 A Doubling [A] doubles the rate of the reaction. However, doubling [B] increases the rate 4  . What is the correct rate law expression? [A][B] Rate k = 3. 2. 4. 1. The rate order on A is one, because a doubling of [A] leads to a doubling of reaction rate. The rate order on B is two, because doubling [B] leads to a 4  = (2) 2 increase in reaction rate. Rate = k [A][B] 2

47. Answers: (a) rate = k [NO] 2 [H 2 ]; (b) k =1.2 M –2 s –1 ; (c) rate = 4.5  10 –4 M /s (a) Determine the rate law for this reaction. (b) Calculate the rate constant. (c) Calculate the rate when [NO] = 0.050 M and [H 2 ] = 0.150 M . BELLWORK The following data were measured for the reaction of nitric oxide with hydrogen:

48. Rate laws (a.k.a. Differential rate laws ) are used to calculate reaction rates when given reactant concentrations. Integrated rate laws are used to calculate the amount of reactants left after a certain amount of time has passed.

57. Second-Order Processes The decomposition of NO 2 at 300 ° C is described by the equation and yields data comparable to this: NO 2 ( g ) NO ( g ) + 1/2 O 2 ( g ) Time ( s ) [NO 2 ], M 0.0 0.01000 50.0 0.00787 100.0 0.00649 200.0 0.00481 300.0 0.00380

62. a) b)

70. = t 1/2 1 k [A] 0

74. SUMMARY Order of reaction Zero First Second Rate law Rate = k Rate = k[A] Rate = k[A] 2 Integrated rate law [A] t = [A] 0 - kt ln[A] t - ln[A] 0 = -kt 1/[A] t - 1/[A] 0 = kt Units of k M/s 1/s 1/(M •s) Linear plot [A] vs. t ln[A] vs. t 1/[A] vs. t slope -k -k k Half life t 1/2 = 1/2[A] 0 k t 1/2 = 0.693/k t 1/2 = 1/(k[A] 0 )

76. Bellwork a)What is the order of the reaction? b)What is the rate law? c) What effect will doubling the initial concentration of A have on the reaction rate?

118. Homogenous catalysts are in the same phase as the reactants. Heterogeneous catalysts are in a different phase than the reactants. Pt, Pd, & Rh metals are used to catalyze gas reactions in a catalytic converter.