Question

For the decomposition of gaseous dinitrogen pentoxide (shownbelow), the rate constant is k = 2.8 10-3 s-1 at 60°C. The initialconcentration of N2O5 is 2.31 mol/L. 2 N2O5(g) 4NO2(g) + O2(g) (a) What is [N2O5] after 5.00 min? _____mol/L (b) What fraction of the N2O5 has decomposed after 5.00 min?

Answer 1

Ao = initial concentration = 2.31 M

A = afetr time concentration = ?

K = 2.8 10-3 s^-1

from rate constant units it is first order reaction

k = 1/t * ln (Ao/A)

2.8 x 10^-3 = 1/5 x 60 * ln (2.31 / A)

ln (2.31 / A) = 0.84

2.31 / A = 2.31

A = 1 M

after 5 min [N2O5] = 1 M

Ao = 2.31 ----------------> initial

A = 1 -------------------> remaining

fraction = Ao - A

            = 2.31 -1

            = 1.31 A

1.31 M [N2O5] decomposed after 5 min

in percent fraction = (1.31 / 2.31 ) x 100

                              = 56.7 %

56.7 % of [N2O5] decomposed after 5 min