In bioenergetics, free energy refers to the portion of a system's energy that is available to do work.
The specific form of free energy used to understand biological reactions is called Gibbs Free Energy (G).
It helps predict whether a chemical reaction will occur spontaneously under constant temperature and pressure.
Gibbs Free Energy (G) is defined by the equation
where:
ΔG = change in free energy,
ΔH = change in enthalpy (total energy),
T = absolute temperature (in Kelvin),
ΔS = change in entropy (disorder).
ΔG helps determine whether a reaction is spontaneous (favorable) or non-spontaneous (unfavourable):
If ΔG<0, the reaction is spontaneous (releases energy).
If ΔG>0, the reaction is non-spontaneous (requires energy input).
If ΔG=0, the system is in equilibrium, and no net energy change occurs.