Question

In an endothermic reaction, $\Delta H$ represents change in enthalpy of a reaction in KJ/mol, the minimum value for energy of activation will be?
A) Less than $\Delta H$
B) Zero
C) More than$\Delta H$
D) Equals to $\Delta H$

Answer 1

Endothermic reaction is the one in which heat is absorbed during the chemical reaction, making the value of $\Delta H$positive. The activation energy is the minimum energy required to break or make the bond in a chemical reaction. $\Delta H$ will be zero in case of equilibrium.

Complete answer:
We will look at the question like this, so in case of endothermic reaction, the forward activation energy is greater than the backward activation energy due to which the value of $\Delta H$ turns out to be positive, thus the minimum activation energy required must be greater than $\Delta H$ .
When the temperature is higher for a chemical reaction, the molecules will have higher collisions leading to higher kinetic energy thus the amount of activation energy will also be higher. In the case of energy profile diagrams, an endothermic reaction has more energy for products than reactants whereas in an exothermic reaction the energy will be more in case of reactants. A catalyst always lowers the activation energy. Do remember this point. If activation energy will become equal to zero that means the reaction is at equilibrium. Also the value of $\Delta H$ will be zero in that case, thus option B is not correct.
Option C) is correct for this question as the minimum value of activation energy should be greater than $\Delta H$ as explained above.

Note:
We have to know that exothermic reactions are the one in which heat is released and the value of $\Delta H$ is negative whereas in an endothermic reaction, heat is being absorbed and the value of $\Delta H$ is positive. A catalyst always lowers the activation energy. If activation energy will become equal to zero that means the reaction is at equilibrium.