Gibbs Free Energy uses enthalpy, temperature, and entropy to predict whether a reaction or process will happen spontaneously or not. Recall that a spontaneous process is one that happens on its own, without needing "help" to go. A non-spontaneous process needs constant "help" to occur. If the Gibbs Free Energy for a process is negative, the process is spontaneous. If the Gibbs Free Energy is positive, the process is non-spontaneous.
It is important to point out that spontaneous does not mean fast; in fact, many spontaneous reactions are extremely slow. For example, the reaction of diamond turning to graphite is a spontaneous reaction, but it is extremely slow. So, we do not need to worry about diamond jewelry turning into graphite!
Watch this video, which describes the Gibbs Free Energy equation and shows how enthalpy, temperature, and entropy work together to determine if a process is spontaneous.
Source: Khan Academy, https://youtu.be/0CTSg82l6rA
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