A chemical reaction is most likely to occur spontaneously if the

- For a spontaneously reaction to takes place, the system must has a negative free-energy change ΔG.

- Because changes in all (free energy - entropy and enthalpy) are related to each other by the following equation:

ΔG = ΔH-TΔS,

So ΔG becomes more negative when entropy (randomness) increases, i. e. when the products of a reaction are more disordered and less complex than the reactants.