(a) Explain the following terms :
(i) Order of a reaction
(ii) Molecularity of a reaction
(b) The rate of a reaction increases four times when the temperature changes from 300 K to 320 K. Calculate the energy of activation of the reaction, assuming that it does not change with temperature .(R = 8.314 J K-1 mol-1 )
(a) (i) Order of a reaction : It is the sum of powers of the molar concentrations of reacting species in the rate equation of the reaction.
(ii) Molecularity of a reaction:
1. It is the total number of reacting species (molecules, atoms or ions) which bring the chemical change.
2. It is always a whole number.
3. It is theoritical concept.
4. It is meaningful only for simple reactions or individual steps of a complex reaction. It is meaningless for overall complex reaction.
(b) Given : = 300K = 320 K
= 4K R= 8.314 Ea= ?
Substituting these values in the formulae,
or log 4 =
or 0.6020 =
or Ea = = 55327.46
Energy of activation, Ea = 55327.46
=55.3 K J mol-1