# Free energy change

 Diagrams of the free energy change for both exergonic and endergonic reactions, indicating that the former is characterized by a negative free energy change (decrease in free energy) and the latter a positive free energy change (increase in free energy).
In thermodynamics, free energy change, ΔG or ΔF, refers to the change in measurement of the free energy, Gibbs free energy G or Helmholtz free energy F, depending on if the system is isothermal-isobaric or isothermal-isochoric, respectively, of a system on passing from the initial state to the final state of the reaction, or on going from reactants to products; in Gibbs free energy terms as:

$\Delta G = G_f - G_i \,$

or in Helmholtz free energy terms as:

$\Delta F = F_f - F_i \,$

the Greek symbol Delta Δ meaning 'change', the subscript f refers to the free energy measure of the system in the final reaction state of the process, and i the free energy measure of the system in the initial reaction state.