(a) 2H2O2 → 2H2O + O2 Rate = k [H2O2] (b) NO2 + CO → NO + CO2 Rate = k [NO2]^2

Question

Determine the order of following reactions from their rate expressions :

(a) 2H₂O₂ → 2H₂O + O₂ Rate = k [H₂O₂]

(b) NO₂ + CO → NO + CO₂ Rate = k [NO₂]²

(c) 2NO + O₂ → 2NO₂ Rate = k [NO]² x [O₂]

(d) CHCl_3(g) + Cl_2(g) → CCl_4(g) + HCl_(g) Rate = k [CHCl₃] [Cl₂]

Answer 1

(a) For the reaction,

2H₂O₂ → 2H₂O + O₂

Since the rate law expression given is,

Rate = k [H₂O₂]

Hence,

The reaction is of first order.

(b) For the reaction,

NO₂ + CO → NO + CO₂

Since the rate law given is Rate = k [NO₂]²,

The reaction is second order with respect to NO₂ and zero order with respect to CO.

Hence the net order of the reaction is,

n = nNO₂ + nco = 2 + 0 = 2

(c) For the reaction,

2NO + O₂ → 2NO₂

Since the rate law expression given is, 

Rate = k[NO]² x [O₂]

The reaction is second order with respect to NO and first order with respect to O₂.

Hence,

The overall order of reaction is n = nNO₂ + no₂ = 2 + 1 = 3.

(d) For the reaction, 

CHCl_3(g) + Cl_2(g) → CCl_4(g) + HCl_(g)

By rate law,

Rate = k [CHCl₃] [Cl₂]

Reaction is first order with respect to CHCl₃ and first order with respect to Cl₂. 

Hence,

The overall order is, 

n = ncHcl₃ + ncl₂ 

= 1 + 1 = 2.