Chem 236-kinetics and kinetic model of gases prep 1) Suppose the half-life is 40

Question

Chem 236-kinetics and kinetic model of gases prep 1) Suppose the half-life is 40.7 s for a first-order reaction and the reactant concentration is 0.0839 M 50.3 s after the reaction starts. How many seconds after the start of the reaction does it take for the reactant concentration to decrease to 0.0085 M? 2) For the reaction 2A(g) + 36(g) C(g) + 2D(g) experimental data was obtained for the rate: the following Run [A] (M) 18] (M) Initial Rate (M/min) 1 0.01 0.2 2 0.01 0.4 3 0.02 0.4 2.2 4.4 17.6 Find the rate law and rate constant.

Explanation / Answer

1)
k = 0.693/half life
= 0.693/(40.7)
= 0.01703 s-1

Integrated rate law is:
ln [A]2 = –k(t2-t1) + ln [A]1
ln (0.0085) = -0.01703*(t2 - 50.3) + ln (0.0839)
0.01703*(t2 - 50.3) = 2.2896
t2 = 184.7 s
Answer: 184.7 s

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