## 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-

H_{2} + Cl_{2} ——-> 2 HCl

Rate = K [H_{2}]^{0} [Cl_{2}]^{0} = K

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

2 NH_{3} ———-> N_{2} + 3H_{2}

Rate = K [NH_{3}]^{0} = K

#### Ex.3) Decomposition of N_{2}O on hot Pt-

N_{2}O————> N_{2} + 1/2 O_{2}

Rate = K [N_{2}O]^{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