Need some understanding this
the decomposition of xy is second order in xy and has a rate constant of 7.02 x 10^-3 m^-1 x s^-1 at a certain temperature.
a) what is the half-life for this reaction at a initial concentration of 0.100 m?
c) if the initial concentration of xy is 0.150m, how long will it take for the concentration to decrease to 0.062 m?

This type of problem is known to be the rate of decay or decomposition. In dealing with this type of problem, we would let Q to be the amount present at any time, Qo as the initial amount, k as the rate constant and then t as the number of hours to reduce the initial amount to the present amount. The equation would be Q=Q0 times e^ -kt.

In letter a, the answer would be 98.7389 seconds. Meanwhile in letter b the answer is 125.8548 seconds. 

the answer for sodium is 0.186

the answer for rubidium is 0.251