Zero order reaction

Zero order reaction

source  : askIITians

Zero order reaction-

Reactions in which the concentrations of the reactants do not change with time and the reaction rate remains constant throughout .Those reactions are zero order reactions.

Ex.1) Photochemical reaction between hydrogen and chlorine-

H₂  +  Cl₂ ——->   2 HCl

Rate = K [H₂]⁰ [Cl₂]⁰ = K

Ex.2 ) Decomposition of  ammonia in presence of Mo or W-

2 NH₃ ———->  N₂    +   3H₂

Rate = K [NH₃]⁰  = K

Ex.3) Decomposition of N₂O on hot Pt-

N₂O————> N₂ + 1/2 O₂

Rate = K [N₂O]⁰  = K

Consider  the reaction,

A——–> B

initial conc.     a             0

For zero order reaction,

Rate = dx / dt = K[A]ⁿ

n = 0

Rate = dx / dt = K[A]⁰ = K

dx = K.dt

Taking integration of both sides,

∫ dx = K ∫ dt

x = Kt + C        ———-eq. 1

C is integration constant

If t= 0 , x=0 then C = 0

Now putting the value of  ‘C’ in eq. 1

x = Kt +0

x = Kt

Characteristics of  zero order reaction-

1) The concentration of the product increases linearly with time. A straight line passing through origin is obtained when  ‘x’  is

plotted against ‘t’ (time).

2) The unit of rate constant ‘K’ is mole litre^-1 time^-1.

3) The time required for the reaction to be complete i-e time at which [A] is zero.

t = initial conc. / K