Decomposition of N2O5 follows first order kinetics and its instantaneous rate is 1.6 x 10^-6 mol/L/s. Calculate the rate constant of the reaction of 0.02M solution.

8×10^-5 s^-1

Explanation:

The decomposition of N2O5 is shown by the reaction equation;

N2O5(aq)⇄NO2(g) + NO3(g)

We have the following information;

Instantaneous rate of reaction = 1.6 x 10^-6 mol/L/s.

Concentration of the N2O5 = 0.02M

Now the rate of decomposition of N2O5 is given by;

R= k[N2O5] (first order reaction)

Hence;

1.6 x 10^-6 mol/L/s = k[0.02M]

k= 1.6 x 10^-6 mol/L/s / 0.02M

k= 8×10^-5 s^-1

Hence the rate of decomposition of N2O5 is 8×10^-5 s^-1

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years