Question

Dimerisation of no2 is an exothermic reaction. If enthalpy of reaction is h, then the minimum value of activation energy for forward reaction (ea) will be

Answer 1

Answer: It will be equal to zero.

Explanation: According to Arrenhius equation,

             K= Ae^ - Ea/RT

where Ea is the activation energy,

If Ea=0, then K=A

Answer 2

Solution:

Dimerisation of $NO_2$ is an exothermic reaction.

For exothermic reactions, enthalpy of reaction is negative.

$\Delta H = -ve\\\\\Delta H = E_a_{(f)} - E_a _{(b)}$

where, $E_a_{(f)} =$ Activation energy for forward reaction

and $E_a_{(b)} =$ Activation energy for backward reaction

For enthalpy to be negative, the minimum value of Activation energy of forward reaction must be equal to zero.

$\Delta H = 0 - E_a _{(b)}\\\\\Delta H = - E_a _{(b)}\\\\\Delta H = -ve$