The usual picture of a chemical reaction in terms of a one-dimensional potential energy
(or reaction coordinate) diagram is shown in Figure 26.24. The vertical axis corresponds
to the energy of the system, and the horizontal axis (reaction coordinate) corresponds to
the geometry of the system. The starting point on the diagram (reactants) is an energy
minimum, as is the ending point (products). Motion along the reaction coordinate is
assumed to be continuous and to pass through a single energy maximum called the transition
state. As described in Section 26.2.1, a transition state on a real many-dimensional
potential energy surface corresponds to a point that is actually an energy minimum in all
but one dimension and an energy maximum along the reaction coordinate.