Question

1. The half-life for the decomposition of substance A is observed to double when the initial concentration of A is halved.

In one particular experiment, you find the half-life to be (5.66x10^2) s when [A]₀ is (1.870x10^-2) M.

Determine the rate constant for the decomposition reaction.

2. Considering the rate of reaction R and the rate constant k for two reactions having different overall orders, which of the following statements is true?

A)	The units of R will be different but the units of k will be the same for the two reactions.

B)	The units of both R and k will be the same for the two reactions.

C)	The units of R will be the same but the units of k will be different for the two reactions.

D)	The units of both R and k will be different for the two reactions.

E)	It is impossible to answer based upon the information provided.

Answer 1

1. The half-life for the decomposition of substance A is observed to double when the initial concentration of A is halved.

In one particular experiment, you find the half-life to be (5.66x10^2) s when [A]0 is (1.870x10^-2) M.

Determine the rate constant for the decomposition reaction.

This must be 2nd order, since it is the only order in which [A]0 is inversely proportional to the half life:

HL = 1/(k*[A]0) , then if [A]0 is halved, the HL will be doubled.

Knowing this

k = 1/(HL*[A]0) = 1/((5.66*10^2)(1.87*10^-2))

k = 0.09448

Q2.

if R = rate of reaction, and k = rate constant for smae overall order:

A) R are always M/s since it is rate (concentraiton change per time)

B) True, since R is always M/s and k is the same for OVERALL orders

C) false, they can't be different

d) false, R is always the same

e) false, we cand do this via dymensional analysis