Question

Part A The reactant concentration in a zero-order reaction was 9.00×10−2 M after 105 s and 1.00×10−2 M after 325 s . What is the rate constant for this reaction? Express your answer with the appropriate units. k0th =

Part B What was the initial reactant concentration for the reaction described in Part A? Express your answer with the appropriate units. [A]0 =

Part C The reactant concentration in a first-order reaction was 6.70×10−2 M after 25.0 s and 2.20×10−3 M after 85.0 s . What is the rate constant for this reaction? Express your answer with the appropriate units. k1st=

Part D The reactant concentration in a second-order reaction was 0.490 M after 125 s and 7.20×10−2 M after 800 s . What is the rate constant for this reaction? Express your answer with the appropriate units. Include an asterisk to indicate a compound unit with multiplication, for example write a Newton-meter as N*m. k2nd =

Answer 1

Part A The reactant concentration in a zero-order reaction was 9.00×10-2 M after 105 s and 1.00×10-2 M after 325 s . What is the rate constant for this reaction? Express your answer with the appropriate units. k0th =

k = ([R2] -[R1]) / (t1-t2)
= (9.00*10^-2 - 1.00*10^-2 ) / (325-105)
= 3.64*10^-4 M/s

Answer: 3.64*10^-4 M/s

Part B What was the initial reactant concentration for the reaction described in Part A? Express your answer with the appropriate units. [A]0 =

for 1st t = 105 s

use:
k =([R0] -[R]) / t
3.64*10^-4 = ([R0] -9.00*10^-2 ) / 105
[R0] = 0.128 M

Answer: 0.128 M

Part C The reactant concentration in a first-order reaction was 6.70×10-2 M after 25.0 s and 2.20×10-3 M after 85.0 s . What is the rate constant for this reaction? Express your answer with the appropriate units. k1st=
USE:
[R2]=[R1]*e^(-k*(t2-t1))
2.2*10^-3= 6.7*10^-2 *e^(-k*(85-25))
2.2*10^-3= 6.7*10^-2 *e^(-k*60)
e^(-k*60) = 0.0328
k*60 = 3.416
k = 0.057 s-1
Answer: 0.057 s-1

Part D The reactant concentration in a second-order reaction was 0.490 M after 125 s and 7.20×10-2 M after 800 s . What is the rate constant for this reaction? Express your answer with the appropriate units. Include an asterisk to indicate a compound unit with multiplication, for example write a Newton-meter as N*m. k2nd =

use:
[R2] = [R1] / (1+K*(t2-t1)*[R1])
7.2*10^-2 = 0.490 / (1+ K*(800-125)*0.490)
7.2*10^-2 = 0.490 / (1+ K*330.75)
(1+ K*330.75)= 6.806
K = 0.0176 M-1s-1
Answer: 0.0176 M-1s-1