Energy of activation of forward and backward reaction are equal in case (numerical calues) where

Options

A. `DeltaH=0`
B. No catalyst present
C. `DeltaS=0`
D. Stoichiometry is the mechanism

Answer

To solve the question regarding the conditions under which the energy of activation of the forward and backward reactions are equal, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Activation Energy**:
- Activation energy (Ea) is the minimum energy required for a reaction to occur. For a reaction, we have two activation energies: one for the forward reaction (Ea forward) and one for the backward reaction (Ea backward).

2. **Using the Relationship**:
- The relationship between the activation energies and the change in enthalpy (ΔH) of the reaction can be expressed as:
\[ \Delta H = E_a^{\text{forward}} - E_a^{\text{backward}} \]

3. **Setting the Activation Energies Equal**:
- According to the problem, we are given that the activation energies for the forward and backward reactions are equal. Let's denote both activation energies as \( x \):
\[ E_a^{\text{forward}} = x \quad \text{and} \quad E_a^{\text{backward}} = x \]

4. **Substituting into the Equation**:
- Substituting these values into the ΔH equation gives:
\[ \Delta H = x - x = 0 \]

5. **Conclusion**:
- Since ΔH equals zero, this indicates that the enthalpy change for the reaction is zero. This typically occurs in a reaction that is at equilibrium, where the energy required to break bonds in the reactants is equal to the energy released when new bonds are formed in the products.

6. **Identifying the Correct Option**:
- The only scenario where the activation energies of both the forward and backward reactions are equal, leading to a change in enthalpy of zero, is option A.

### Final Answer:
- The correct option is **A**, where the activation energy of the forward and backward reactions are equal, resulting in a change in enthalpy (ΔH) of zero.