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Difficulty: MediumActivation Energy and Energy Profile Diagrams

In chemical kinetics and energetics, potential energy profile diagrams illustrate key energy values along a reaction pathway. Match each parameter of an energy profile diagram on the left with its correct chemical definition or significance on the right.

  • Activation energy of the forward reaction (Ea,fE_{a,\text{f}})Energy difference between the activated complex peak and the reactants
  • Transition state (Activated complex)High-energy, unstable species formed at the maximum potential energy point
  • Enthalpy change of reaction (ΔH\Delta H)Difference between potential energy of products and potential energy of reactants
  • Action of a positive catalystProvides an alternate reaction path with a lower peak activation barrier

Answer

Activation energy of forward reaction matches the energy difference between the activated complex peak and reactants. Transition state matches the high-energy, unstable species formed at the maximum potential energy point. Enthalpy change of reaction matches the difference between product potential energy and reactant potential energy. Action of a positive catalyst matches providing an alternate reaction path with a lower peak activation barrier.
The parameters are matched according to standard kinetic definitions: forward activation energy measures the height of the energy barrier from the reactants; the transition state is the highest energy activated complex; enthalpy change is the net potential energy difference between products and reactants; and a catalyst lowers the activation energy barrier.

Step-by-Step Solution

1
Determine the physical meaning of forward activation energy (Ea,fE_{a,\text{f}}).
It is the minimum energy required to boost reactants to the transition state peak.
Reactant molecules must overcome this energy barrier to undergo effective collisions.
2
Identify the feature located at the highest point of the energy profile diagram.
The apex represents the transition state (activated complex).
This configuration has maximum potential energy and minimum stability along the reaction coordinate.
3
Relate total enthalpy change (ΔH\Delta H) to potential energy values on the diagram.
ΔH\Delta H equals the potential energy of products minus potential energy of reactants.
Enthalpy change depends purely on the net difference between final and initial energy states.
4
Analyze how addition of a positive catalyst affects energy parameters.
It lowers the peak height by introducing a new reaction pathway.
Catalysts alter the mechanism and lower activation energy without changing initial or final energy levels.

Key Concept

Activation Energy and Energy Profile Diagrams
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Activation Energy and Energy Profile Diagrams