The activation energy of exothermic reaction `ArarrB` is 80 kJ `"mol"^(-1)` . The heat of reaction is `200 kJ "mol"^(-1)`. The activation energy for the reaction`Brarra` ( in kJ/mol) will be :

Options

A. 80
B. 120
C. 40
D. 280

Explanation

To find the activation energy for the reverse reaction \( B \rightarrow A \), we can use the relationship between the activation energies of the forward and reverse reactions and the heat of reaction.

### Step-by-Step Solution:

1. **Understand the Given Information**:
- Activation energy for the forward reaction \( A \rightarrow B \) (denoted as \( E_{A \rightarrow B} \)) = 80 kJ/mol.
- Heat of reaction (denoted as \( \Delta H \)) = -200 kJ/mol (since it is an exothermic reaction, we take it as negative).

2. **Use the Relationship Between Activation Energies**:
The relationship between the activation energies of the forward and reverse reactions is given by:
\[ \Delta H = E_{A \rightarrow B} - E_{B \rightarrow A} \]
where \( E_{B \rightarrow A} \) is the activation energy for the reverse reaction.

3. **Substitute the Known Values**:
Plugging in the values we have:
\[ -200 = 80 - E_{B \rightarrow A} \]

4. **Rearrange the Equation**:
To find \( E_{B \rightarrow A} \), rearrange the equation:
\[ E_{B \rightarrow A} = 80 + 200 \]

5. **Calculate the Activation Energy for the Reverse Reaction**:
\[ E_{B \rightarrow A} = 280 \text{ kJ/mol} \]

### Final Answer:
The activation energy for the reaction \( B \rightarrow A \) is **280 kJ/mol**.

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