An endothermic reaction, A→ B has an activation energy 15 kcal/mol and energy of the reaction is 5 kcal/mol. The activation energy of the reaction, B → A is:

The activation energy of the reverse reaction (B → A) can be calculated using the given information about the forward reaction (A → B).

Step 1: Understand the given information

• The activation energy of the forward reaction (A → B) is 15 kcal/mol. This is the energy required to start the reaction.
• The energy of the reaction (also known as the enthalpy change, ΔH) is 5 kcal/mol. Since it's given as a positive value, we know the reaction is endothermic, meaning it absorbs heat.

Step 2: Calculate the activation energy of the reverse reaction

• The activation energy of the reverse reaction (B → A) is the sum of the activation energy of the forward reaction and the energy of the reaction. This is because for the reaction to go in reverse, it needs to overcome the forward activation energy and also supply the energy difference of the reaction.
• So, the activation energy of the reverse reaction = activation energy of the forward reaction + energy of the reaction
• Therefore, the activation energy of B → A = 15 kcal/mol + 5 kcal/mol = 20 kcal/mol.

So, the activation energy of the reaction B → A is 20 kcal/mol.