A reaction has a rate constant of 0.0185 s-1 and the only reactant has an initial concentration of 0.135 M. What is the concentration in molarity of this reactant after 125 seconds?

Question

A reaction has a rate constant of 0.0185 s-1 and the only reactant has an initial concentration of 0.135 M. What is the concentration in molarity of this reactant after 125 seconds?

A. 4.84 * 10-5

B. 0.0134

C. 0.103

D. 0.310

E. 4.84

Answer 1

From the units of the rate constant (s^-1), we can tell it is a first order reaction.

The integrated rate law for a first order reaction can be written as ln [A] = -kt + ln [A]_o

ln [A] = - (0.0185 s^-1)(125 s) + ln [0.135 M]

ln [A] = -2.3125 - 2.00 = -4.3125

[A] = 0.0134 M ANSWER B