Chapter 3: Rate Laws

More on Activation Energy

The activation energy can be thought of as a barrier to the reaction. One way to view the barrier to a reaction is through the reaction coordinates. These coordinates denote the energy of the system as a function of progress along the reaction path. For the reaction

\( \text{A} + \text{BC} \rightleftharpoons \text{A} \cdots \text{B} \cdots \text{C} \rightarrow \text{AB} + \text{C} \)

the reaction coordinate is

Reaction energy diagram showing energy versus reaction progress. The diagram starts with reactants labeled A+BC, rises to a peak indicating the transition state (A...B...C) with an activation energy (E_A) marked, and declines to the products AB+C. The energy difference between reactants and products is labeled as ΔH_rx. Arrows near the peak suggest molecular vibrations during the transition state.

Progress along reaction path

We see that for the reaction to occur, the reactants must overcome an energy barrier or activation energy EA.

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