Activation Energy of the Reaction C + D → A + B

Introduction:
Activation energy is the minimum amount of energy required for a chemical reaction to occur. It is the energy barrier that must be overcome for reactant molecules to convert into products. In this case, we are given the activation energy for the reaction A + B → C + D as 20 kcal.

Explanation:
To determine the activation energy for the reverse reaction C + D → A + B, we can make use of the principle of microscopic reversibility, which states that the activation energy for the forward and reverse reactions are equal in magnitude but opposite in sign.

Principle of Microscopic Reversibility:
The principle of microscopic reversibility states that if a reaction occurs via a particular pathway with a certain activation energy, then the reverse reaction occurs via the same pathway with the same activation energy but opposite in sign.

Activation Energy Calculation:
Since we are given the activation energy for the forward reaction as 20 kcal, the activation energy for the reverse reaction can be determined by reversing the sign:

Activation energy of the forward reaction (A + B → C + D) = +20 kcal

Activation energy of the reverse reaction (C + D → A + B) = -20 kcal

Therefore, the activation energy of the reaction C + D → A + B is -20 kcal.

Conclusion:
The activation energy of a chemical reaction is an important factor that determines the rate at which the reaction occurs. In this case, the activation energy for the reverse reaction C + D → A + B is determined to be -20 kcal, which indicates the energy barrier that must be overcome for the conversion of C + D into A + B. The principle of microscopic reversibility allows us to relate the activation energies of the forward and reverse reactions, providing valuable insights into the energetics of chemical reactions.