Question

In the equilibrium, A + B $\rightleftharpoons$ C + D, the activation energy for the forward reaction is 25 Kcal / mol and that of backward reaction is 15 Kcal / mol. Which one of the following statements is correct?
(a)- It is an exothermic reaction
(b)- It is an endothermic reaction
(c)- It is a reaction for which $\Delta H=0$
(d)- It is a sublimation process

Answer 1

Activation energy is the energy required to complete the reaction, with the help of activation energy we can find the type of reaction i.e., either endothermic or exothermic reaction. Exothermic are those in which the products are formed and the release of energy takes place. Endothermic are those reactions in which the products are formed when energy is supplied to the reaction.

Complete step by step solution:
- Activation energy is the energy required to complete the reaction, with the help of activation energy we can find the type of reaction i.e., either endothermic or exothermic reaction.
- We can find the reaction as exothermic or endothermic with activation energy as the energy used in forward and backward reactions. Exothermic are those in which the products are formed and the release of energy takes place. Endothermic are those reactions in which the products are formed when energy is supplied to the reaction.
- When the energy used for the forward reaction is less than the energy used for the backward reaction, then the reaction is exothermic. When the energy used for the forward reaction is more than the energy used for the backward reaction, then the reaction is an endothermic reaction.
So, the formation of C + D requires 25 Kcal/mol, and in the formation of A + B requires 15 Kcal/mol, therefore the reaction will be an endothermic reaction.
So, the correct answer is “Option B”.

Note: We can also find the type of reaction by taking the difference in energy of the forward reaction and backward reaction, if the value of positive then the reaction is endothermic, and if the value of negative then the reaction is exothermic. And if the difference is zero, then the reaction is in equilibrium.