Question

In terms of entropy and the real world, what is the end result of a spontaneous process?

Answer 1

A spontaneous reaction is one which occurs with no outside intervention.

In terms of thermodynamics, a spontaneous reaction is one where the change in Gibbs free energy, ΔG, has a negative value. That is, the Gibbs free energy of the products is less than for the reactants.

The change in Gibbs free energy depends on both the change in enthalpy, ΔH, and the change in entropy, ΔS, along with the temperature.

ΔG = ΔH - TΔS


Esther's statement about the second law of thermodynamics isn't quite correct. The second law states that an isolated system will spontaneously move toward equilibrium where entropy is at a maximum. That isn't quite the same as Esther's statement. That's because a reaction can be spontaneous even with a decrease in entropy. A decrease in entropy is negative. That makes -TΔS positive, but if ΔH is sufficiently negative, then ΔG is negative and the reaction is spontaneous, even as entropy decreases.