An exothermic reaction X → Y has an activation energy 30 kJ mol . If energy change ∆ E during the re — Chemical Kinetics Chemistry Question
Question
An exothermic reaction X → Y has an activation energy 30 kJ mol . If energy change ∆ E during the reaction is –20 kJ, then the activation energy for the reverse reaction in kJ is _____. –1
💡 Solution & Explanation
**Step 1: Identify the given information** - Forward reaction (X → Y) activation energy: Ea(forward) = 30 kJ/mol - Energy change: ΔE = –20 kJ/mol (exothermic, so products are lower in energy) **Step 2: Apply the relationship between activation energies and energy change** The key relationship is: $$\Delta E = E_a(\text{forward}) - E_a(\text{reverse})$$ **Step 3: Rearrange to solve for reverse activation energy** $$E_a(\text{reverse}) = E_a(\text{forward}) - \Delta E$$ **Step 4: Substitute the values** $$E_a(\text{reverse}) = 30 - (-20)$$ $$E_a(\text{reverse}) = 30 + 20$$ $$E_a(\text{reverse}) = 50 \text{ kJ/mol}$$ **Step 5: Verify the logic** Since the forward reaction is exothermic (ΔE = –20 kJ), the reverse reaction must be endothermic and require more energy to proceed. An activation energy of 50 kJ for the reverse reaction (greater than the forward 30 kJ) confirms this makes physical sense. Therefore, the answer is 50.00.