Question

A reactant decomposes with a half-life of 129 s when its initial concentration is 0.380 M. When the initial concentration is 0.504 M, this same reactant decomposes with the same half-life of 129 s. A. What is the value and unit of the rate constant (k) for this reaction? B. What is the order of the reaction?a. 0.b. 1. c. 2

Answer 1

A) The rate constant is 0.0078 s^-1

B) The order of the reaction is 1

Step-by-step explanation:

A) Rate constant (k) = Rate ÷ final concentration

Rate = change in concentration/half-life

Initial concentration of reactant = 0.38 M

Half-life is the time taken for the reactant to decompose to half of its initial concentration = 129 s

Final concentration = 1/2 × 0.38 = 0.19 M

Change in concentration = 0.38 - 0.19 = 0.19 M

Rate = 0.19/129 = 0.0015 M/s

Rate constant (k) = 0.0015 M/s ÷ 0.19 M = 0.0078 s^-1

B) Rate = kC^n

n is the order of the reaction

0.0015 = 0.0078×0.19^n

0.19^n = 0.0015/0.0078

0.19^n = 0.19

Log 0.19^n = Log 0.19

nLog 0.19 = Log 0.19

n = Log 0.19/Log 0.19 = 1