What is the free energy of a chemical reaction and how does it relate to spontaneity?

The free energy of a chemical reaction is the amount of energy available to do work. It relates to spontaneity through the change in free energy (∆G) of a reaction.

Spontaneous reactions have a negative ∆G, meaning they release energy and are energetically favourable. Non-spontaneous reactions have a positive ∆G, meaning they require energy input and are energetically unfavourable.

The ∆G of a reaction is determined by the difference between the free energy of the products and the free energy of the reactants. This difference is influenced by both the enthalpy (∆H) and entropy (∆S) of the reaction.

If ∆H is negative and ∆S is positive, the reaction is spontaneous at all temperatures. If ∆H is positive and ∆S is negative, the reaction is non-spontaneous at all temperatures. If ∆H is positive and ∆S is positive, the reaction is spontaneous at high temperatures but non-spontaneous at low temperatures.

The ∆G can also be used to determine the equilibrium constant (K) of a reaction. If ∆G is negative, K is greater than 1 and the reaction favours the products. If ∆G is positive, K is less than 1 and the reaction favours the reactants. If ∆G is zero, K is equal to 1 and the reaction is at equilibrium.

Overall, the free energy of a chemical reaction is a key factor in determining its spontaneity and equilibrium constant.