(a) The decomposition of N2O5(g) is a first order reaction with a rate constant of 5 x 10–4 sec–1 at 45°C.
i.e., 2N2O5(g) = 4NO2(g) + O(g)
If initial concentration of N2O5 is 0.25, calculate its concentration after two minutes. Also calculate half life for the decomposition of N2O5(g).
(b) For an elementary reaction: 2A + B → 3C The rate of appearance of C at time ‘t’ is 1.3 x 10–4 mol l–1 s–1. Calculate at this time:
(i) Rate of reaction (ii) Rate of disappearance of A.
Rate constant K = 5 x 10–4 sec. Initial concentration [A]0 = 0.25 M Final concentration [A]t =? Time taken by the reaction, t = 2 min.
For a first order reaction, rate constant (K) is given by
(i) The rate of appearance of C at time t
(ii) Rate of disappearance of A
This reaction follows second order kinetics.
So that, the rate equation for this reaction will
Rate, R = k[X]2 .............(1)
Let initial concentration is x mol L−1,
Plug the value in equation (1)
Rate, R1 = k .(a)2
Given that concentration is increasing by 3 times so new concentration will 3a mol L−1
Plug the value in equation (1) we get
Rate, R2 = k (3a)2
We have already get that R1 = ka2 plus this value we get
R2 = 9 R1
So that, the rate of formation will increase by 9 times.
Rate = k[A]2
If concentration of X is increased to three times,
Rate = k[3A]2
or Rate = 9 k A2
Thus, rate will increase 9 times.