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Difficulty: EasyActivation Energy and Energy Profile Diagrams

In a chemical reaction, the potential energy of the reactants is 45 kJ mol−145\text{ kJ mol}^{-1}, while the potential energy of the activated complex at the peak of the energy profile diagram is 125 kJ mol−1125\text{ kJ mol}^{-1}. What is the activation energy for the forward reaction in kJ mol−1\text{kJ mol}^{-1}?

Answer: 80 kJ mol^{-1}

Answer

The activation energy for the forward reaction is 80 kJ mol^{-1}.
The activation energy (EaE_a) for a forward chemical reaction is defined as the difference in energy between the activated complex (peak of the energy profile) and the reactants. Subtracting the reactant potential energy (45 kJ mol−145\text{ kJ mol}^{-1}) from the activated complex potential energy (125 kJ mol−1125\text{ kJ mol}^{-1}) gives an activation energy of 80 kJ mol−180\text{ kJ mol}^{-1}.

Step-by-Step Solution

1
Identify the potential energy levels of the reactants and the activated complex from the given data.
Energy of reactants = 45 kJ mol^{-1}; Energy of activated complex = 125 kJ mol^{-1}
Forward activation energy depends directly on the difference between these two energy states.
2
Subtract the potential energy of the reactants from the potential energy of the activated complex.
Ea = 125 kJ mol^{-1} - 45 kJ mol^{-1} = 80 kJ mol^{-1}
The activation energy represents the minimum energy barrier that reacting particles must overcome to reach the transition state.

Key Concept

Forward Activation Energy Calculation from Energy Profile Data
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Topics

Activation Energy and Energy Profile Diagrams