the strontium90 presently on earth to be reduced to 100 of t

the strontium-90 presently on earth to be reduced to 1.00% of the present amount? Radioactive decay follows first-order kinetics. 5) The decomposition of NO2 follows second-order kinetics and had a rate constant equal to 1.4 × 10-s Ms-1. (a) If 4.0 mol of NO2 is initially present in a 2.0 L vessel, what concentration of NO2 remains after 2.0 hr? (b) Referring to the conditions in part (a), what is the half-life of the reaction?

Solution

rate constant = k = 1.4x10^-5 M-1 s-1

a)

number of moles of NO2 = 4.0mole

volume = 2.0L

Concentration of NO2 = number of moles/volume = 4.0/2.0 = 2.0 M

Initial concentration of NO2 = [A]0 = 2.0M

Remaining concentration of NO2 = [A]t = ?

time = 2.0 hour= 2.0x60x60 sec= 7200 seconds

for second order reaction

1/[A]t = Kt + 1/[A]0

             = (1.4x10^-5 x 7200 )+ 1/2.0

           = 0.6008M

remaining concentration of NO2 = 0.6008M

for second order

half-life=1/kx[A]0

Half-life = 1/1.4x10^-5 x2.0

half-life = 0.357x10^5 seonds

Half-life = 9.917 hours