At constant temperature and pressure, the relationship between ∆Suniv (the change in the entropy of the universe) and ∆Gsys (the change in the Gibbs free energy of the system) can be described by the following equation:
∆Suniv = ∆Gsys / T
where T is the temperature in Kelvin.
This equation is derived from the second law of thermodynamics, which states that the entropy of the universe tends to increase for any spontaneous process. The Gibbs free energy of a system, on the other hand, tells us whether a reaction is thermodynamically favorable or not. If ∆Gsys is negative, the reaction is spontaneous and thermodynamically favorable, while if ∆Gsys is positive, the reaction is non-spontaneous and thermodynamically unfavorable.
The equation above shows that as the change in the Gibbs free energy (∆Gsys) becomes more negative (i.e. more thermodynamically favorable), the change in the entropy of the universe (∆Suniv) increases. This means that a spontaneous reaction that releases energy (negative ∆Gsys) will also tend to increase the entropy of the universe, while a non-spontaneous reaction that requires energy input (positive ∆Gsys) will tend to decrease the entropy of the universe.