Question

For an endothermic reaction, energy of activation is E${}_a$ and enthalpy of reaction is H (both of these in kJ/mol). Minimum value of E${}_a$ will be:

• A. less than H
• B. equal to H
• C. more than H
• D. equal to zero

Answer 1

The correct option is C more than H

Activation energy is the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction.

(Image)

$E_a$-Activation energy

Here, energy of products is higher than that of reactants.

This graph is for an endothermic reaction.

$△H$ for an endothermic reaction is positive

See figure above, when the reaction reaches point P, the reactants possess enough energy for the reaction to take place.

In further reaction, some energy is use up for conversion of reactants to products.

This used up energy must be less than $E_a$, for an endothermic reaction

Since,

$E_a$- H = (used up energy)

$\therefore E_a>H$

Hence, the activation energy must be more than H