Answer is: <span>- delta G. </span>The change in Gibbs free energy (ΔG), at constant temperature and pressure, is: <span>ΔG=ΔH−TΔS. </span>ΔH<span> is the change in enthalpy. </span>ΔS is change in entropy. T is temperature of the system. When ΔG is negative, a reaction (<span>occurs without the addition of external energy)</span><span> will be spontaneous (</span>exergonic).