Question

A reaction A B has the following time dependence for the concentration of [A] vs time. For t=(0 s, 5 s, 10 s, 15 s, 25 s) the concentration of [A]=(30.00 M, 19.81 M, 13.08 M, 8.64 M, 3.77 M). The initial concentration of [A] is the value at t=0 s. (A)Calculate the values of the rate constant k assuming that the reaction is first order. What is the value of k at 5 s? s-1 What is the value of k at 10 s? s-1 What is the value of k at 15 s? s-1 What is the value of k at 25 s? s-1 (B)Calculate the value of k assuming that the reaction is second order. What is the value of k at 5 s? M-1s-1 What is the value of k at 10 s? M-1s-1 What is the value of k at 15 s? M-1s-1 What is the value of k at 25 s? M-1s-1 (C)Use your results from parts A and B above to decide what the order of the reaction is for your data. (Enter 1 or 2) (D)What is the concentration of [A] at time t=72 s? M

Answer 1

at 5 sec^-1 k = 1/t ln(A_0/A_t) = 1/5 ln(30/1981) = 0.083 sec^-1 at 10 sec^-1 k = 1/10 ln(30/8.64) = 0.083 sec^-1 at 25sec^-1 k = 1/25 ln(30/377) = 0.083 sec^-1 at 25sec k = 1/25 ln [30/377) = 0.083 sec^-1 at 5 sec k = 1/t [1/A_t - 1/A_0] = 1/5 [1/1981 - 1/30] at 10sec^-1 k = 1/10 [1/13.08 - 1/30] [= 3.43 times 10^-3 M^-1 sec] = 4.31 times 10^-3 m^-1 sec^-1 at sec^-1 K = 1/15 [1/8.64 - 1/30] = 5.5 times 10^-1 M^-1 sec^-1 at 25 sec^-1 K = 1/25 [1/3.77 - 1/30] = 9.28 times 10^-3 M^-1 sec^-1