The `E_a` for forward reaction is 50 kcal. The `E_a` for its backward reaction is:

Options

A. equal 50 kcal
B. greater than 50 kcal
C. less than 50
D. either greater or less than 50

Answer

To determine the activation energy for the backward reaction given the activation energy for the forward reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- The activation energy (Ea) is the minimum energy required for a reaction to occur.
- The forward reaction is the reaction that proceeds from reactants to products.
- The backward reaction is the reverse process, going from products back to reactants.

2. **Given Information**:
- The activation energy for the forward reaction (Ea forward) is given as 50 kcal.

3. **Relationship Between Forward and Backward Activation Energies**:
- The relationship between the activation energies of the forward and backward reactions is influenced by the enthalpy change (ΔH) of the reaction.
- The equation that relates these energies is:
\[ \Delta H = E_a^{\text{forward}} - E_a^{\text{backward}} \]
- Rearranging gives:
\[ E_a^{\text{backward}} = E_a^{\text{forward}} - \Delta H \]

4. **Determine the Nature of the Reaction**:
- If the reaction is **exothermic** (releases energy), ΔH is negative, which means:
\[ E_a^{\text{backward}} > E_a^{\text{forward}} \]
- If the reaction is **endothermic** (absorbs energy), ΔH is positive, which means:
\[ E_a^{\text{backward}} < E_a^{\text{forward}} \]

5. **Conclusion**:
- Since we do not have information about whether the reaction is exothermic or endothermic, we cannot definitively state whether the activation energy for the backward reaction is greater than or less than 50 kcal.
- Thus, the activation energy for the backward reaction could either be greater than or less than 50 kcal, depending on the nature of the reaction.

6. **Final Answer**:
- Therefore, the correct option is that the activation energy for the backward reaction is either greater or less than 50 kcal.