How can one determine the free energy change in a system without any cost involved?

One can determine the free energy change in a system without any cost involved by using the equation: G H - TS, where G is the change in free energy, H is the change in enthalpy, T is the temperature in Kelvin, and S is the change in entropy. This equation allows for the calculation of free energy change based on the enthalpy and entropy changes in the system at a given temperature.