
Reaction coordinate showing two possible directions of spontaneous reactions; the region in red depicting a reaction quantified by a negative free energy change (ΔG < 0) of products on going to reactants, otherwise referred to as an exergonic reaction. [1]

Reaction coordinate (negative free energy change)

Reaction coordinate showing two possible directions of spontaneous reactions; the region in red depicting a reaction quantified by a negative free energy change (ΔG < 0) of products on going to reactants, otherwise referred to as an exergonic reaction. [1]

In chemistry, a negative free energy change refers to a reaction or process in which the free energy, Gibbs or Helmholtz, in the reactants in initial state, Gi or Fi, is greater in value that the free energy of the products in the final state, Gf or Ff.

For isothermal-isobaric (typical earth-bound) systems, negative free energy change is stated mathematically as:

where the symbol ΔG or free energy change is defined mathematically as:

$\Delta G = G_f - G_i \,$

References
1. Thims, Libb. (2007). Human Chemistry (Volume One) (graph, pg. 113). Morrisville, NC: LuLu.