How can I draw an elementary reaction in a potential energy diagram?

1 Answer
Ernest Z.
Jun 26, 2015

You join the potential energy diagrams into one diagram.

Explanation:

A potential energy diagram represents the energy pathway for an elementary reaction — a single-step process.

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Many reactions take place in a series of steps.

For example, the starting materials ("SM") may first react to form some intermediate
("I"), which then reacts further to form the products ("P").

We would write the reaction as occurring in two steps:

Step 1: "SM" → "I"

Step 2: "I" → "P"

Overall: "SM" → "P"

Step 1 is an elementary reaction, so we draw a potential energy diagram going from "SM" to "I" through a transition state "TS"_1 — the left portion of the diagram below.

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Step 2 is another elementary reaction, so we draw a potential energy diagram going from "I" to "P" through a transition state "TS"_2.

But the starting point for Step 2 is the ending point for step 1, so we join the two diagrams together to make a double-hump curve as shown above.

Each hump represents the transition state for a separate elementary reaction.

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