A reaction that leads to a decrease in the free energy of the system is always spontaneous.

Yes, that's correct. A reaction that leads to a decrease in the free energy of the system is always spontaneous. This is based on the principle of thermodynamics. The free energy, also known as Gibbs free energy (G), is a measure of the potential for reversible or maximum work that can be done by a system at constant temperature and pressure.

Here are the steps to understand this:

1. The change in free energy (ΔG) during a reaction is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy (heat energy), T is the absolute temperature, and ΔS is the change in entropy (disorder).

2. If ΔG is negative, the reaction will proceed spontaneously in the forward direction. This is because the system is losing energy and becoming more stable.

3. If ΔG is positive, the reaction is non-spontaneous as it is. However, it could proceed spontaneously in the reverse direction.

4. If ΔG is zero, the reaction is at equilibrium, with no net change taking place over time.

So, a decrease in the free energy of the system (negative ΔG) indicates a spontaneous reaction.