Question

The activation energy of exothermic reaction $A→ B$ is 80 kJ $mol^-1$. The heat of reaction is 200 kJ $mol^-1$. The activation energy for the reaction $B→ A$ (in kJ $mol^-1$) will be ________.

• A. 80
• B. 120
• C. 40
• D. 280

Hint:

The activation energy of exothermic reaction $A→ B$ is 80 kJ $mol$. The activation energy for the reaction $B→ A$ (in kJ $mol$) will be ____.

Answer 1

The Correct Option is D

Step 1: Formula
For any reaction, the relationship between forward activation energy ($E_{af}$), backward activation energy ($E_{ab}$), and enthalpy change ($\Delta H$) is: $\Delta H = E_{af} - E_{ab}$.
Step 2: Values
$E_{af} = 80 \text{ kJ } mol^{-1}$.
Since the reaction is exothermic, the heat released is 200 kJ, so $\Delta H = -200 \text{ kJ } mol^{-1}$.
Step 3: Calculation
$-200 = 80 - E_{ab}$
$E_{ab} = 80 + 200 = 280 \text{ kJ } mol^{-1}$.
Final Answer: (D)