For a process to occur spontaneously, the system free energy or chemical potential of the system :

For a process to occur spontaneously, the system's free energy or chemical potential must decrease. This is based on the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible.

Here are the steps to understand this:

1. Free energy (G) is a thermodynamic potential that measures the maximum reversible work that a system can perform at constant temperature and pressure. It is given by the equation G = H - TS, where H is the enthalpy, T is the absolute temperature, and S is the entropy.

2. A spontaneous process is one that occurs without ongoing outside intervention. In terms of free energy, a process is spontaneous if the change in free energy (ΔG) is negative. This is known as the Gibbs free energy change.

3. The chemical potential (μ) is a form of potential energy that can be absorbed or released during a chemical reaction. It is the change in free energy per particle added to the system, at constant entropy and volume.

4. For a process to be spontaneous, the chemical potential of the system must also decrease. This is because a decrease in chemical potential means the system is moving towards a lower, more stable energy state.

5. Therefore, for a process to occur spontaneously, the system's free energy or chemical potential must decrease. This is a fundamental principle of thermodynamics and underlies the direction and feasibility of chemical reactions.