In thermodynamics, Gibb's free energy is the quantitative measure of the <u>spontaneity or feasibility </u>of a chemical reaction, at fixed temperature and pressure.
It can also be described as the <u>maximum available work obtained from a closed system</u>. This maximum work can only be achieved in a reversible process, <u>at fixed pressure and temperature.</u>
<u>The Gibb's free energy (ΔG) is given by</u>: ΔG = ΔH - T.ΔS