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Chemical Kinetics

Question
CBSEENCH12006325
Wired Faculty App

(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.

Solution

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
                        K = 2.303tlog A0At


5×10-4 = 2.303tlog0.25At5×10-4×22.303 = log 0.25 - logAt           0.0004  = log 0.25 - logAt           0.0004 = 0.3979 - log At0.0004 - 0.3979 = -logAt              -0.3975 = -logAt                         At = antilog (0.3975)                          At = 2.6


(b) 2A+B →  C

(i) The rate of appearance of C at time t

                              = 1.3 × 10-4 mol L-1 s-1

-ddt[C] = 12ddtA = +12ddtB

(ii) Rate of disappearance of A

                  = 2 × 1.3 × 10-4 mol L-1 S-1=2.6 × 10-4 mol L-1 S-1.

                    




































































































































Some More Questions From Chemical Kinetics Chapter

What will be the effect of temperature on rate constant?

A reaction is 50% complete in 2 hours and 75% complete in 4 hours. What is the order of the reaction.

The rate law for the decomposition of N2O5 is rate = k[N2O5]. What is the significance of k in this equation?

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