Question

The rate constant for a zero order reaction A → products is 0.0030 mol L$^{-1}$ s$^{-1}$. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075 M?

• A. 10 s
• B. 20 s
• C. 8.33 s
• D. 1.33 s

Hint:

For zero order reactions, time is directly proportional to the drop in concentration.

Answer 1

The Correct Option is C

For a zero order reaction, the integrated rate law is: $[A]_t = [A]_0 - kt$ Rearranged: $t = \dfrac{[A]_0 - [A]_t}{k}$
Substitute: $[A]_0 = 0.10$ mol/L, $[A]_t = 0.075$ mol/L, $k = 0.0030$ mol L$^{-1}$ s$^{-1}$
$t = \dfrac{0.10 - 0.075}{0.0030} = \dfrac{0.025}{0.0030} = 8.33$ s