For a reaction A → B, enthalpy of reaction is -4.2 kJ mol⁻¹ and enthalpy of activation is 9.6 kJ mol

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Question

For a reaction A → B, enthalpy of reaction is -4.2 kJ mol⁻¹ and enthalpy of activation is 9.6 kJ mol⁻¹. The correct potential energy profile for the reaction is shown in option.

Accepted Answer

Correct Answer: C — Graph 3Step-by-step Solution:Since the enthalpy of reaction DeltaH = -4.2 kJ/mol (negative), the reaction is exothermic: products lie at a lower energy level than reactants. The forward activation energy Ea(forward) = 9.6 kJ/mol. The reverse activation energy: Ea(reverse) = Ea(forward) + |DeltaH| = 9.6 + 4.2 = 13.8 kJ/mol. The correct profile must show: (1) products lower than reactants, and (2) forward activation energy (9.6) less than reverse activation energy (13.8). Graph 3 satisfies both conditions.Why other options are incorrect: Graph 1 shows products at higher energy (endothermic), contradicting DeltaH = -4.2 kJ/mol. Graph 2 likely shows products lower but with incorrect relative activation energies. Graph 4 does not match the given data.Key Concept: For an exothermic reaction: DeltaH = Ea(forward) - Ea(reverse) (negative). Therefore: Ea(reverse) = Ea(forward) - DeltaH = Ea(forward) + |DeltaH|. In the energy profile, the transition state is a peak, products lie below reactants for exothermic reactions.

For a reaction A → B, enthalpy of reaction is -4.2 kJ mol⁻¹ and enthalpy of activation is 9.6 kJ mol⁻¹. The correct potential energy profile for the reaction is shown in option.

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For a reaction A → B, enthalpy of reaction is -4.2 kJ mol⁻¹ and enthalpy of activation is 9.6 kJ mol⁻¹. The correct potential energy profile for the reaction is shown in option.

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