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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