Reaction coordinate

Reaction coordinate (labeled) 3

In chemistry, reaction coordinate is a name that refers typically to the plotting of one variable of a chemical reaction on the y-coordinate, typically energy or free energy, versus the another variable, such as extent of reaction, species concentration, reaction velocity, etc., on the x-coordinate. Reaction coordinates originated from transition state theory, wherein surface energy plots were developed as a conceptual tool.

The following are some examples:

Reaction coordinateDrug receptor (free energy reaction coordinate)SN2 reaction diagram
Reaction coordinate depicting the initial state of the reactants on going to the final state of the products through two different pathways, indicating that state variables are path-independent.
A typical drug-receptor reaction coordinate as are used on drug-receptor thermodynamics, showing the activated complex.
An SN-2 reaction coordinate, showing the intermediate transition state.
Reaction coordinate (negative free energy change)

A generic reaction coordinate, showing that reaction can be spontaneous in both directions (meaning it can just as easily unravel as did it form), and the red area indicating a region of negative free energy change.

External links
Reaction coordinate – Wikipedia.
Reaction coordinate – IUPAC Gold Book.

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