# Organic Chemistry/Introduction to reactions/Gibbs free energy

**Gibbs free energy** is represented by the following equation:

**ΔG = ΔH -TΔS**

- ΔG is the change in Gibbs free energy.
- ΔH is the change in potential energy, sometimes known as the enthalpy of a system.
- T is the temperature in Kelvin.
- ΔS is a statistical correlation, known as the entropy of a system.

The basic principle is that *total* entropy increases. This increase can be because of an increase in the entropy of the chemicals, *ΔS*, or because the reaction has produced heat, increasing the entropy of the environment.

The Gibbs free energy lets us calculate the total increase in entropy, including the effects on the environment, without needing to know anything about the environment.

At *low* temperatures, *ΔG* is approximately *ΔH*, and nature favours the reaction with lowest energy products, which release the most heat. This may *reduce* the entropy of the *system*, but the *increase* in the entropy of the *environment* more than compensates.

At *high* temperatures, *ΔG* is approximately *-TΔS*, and nature favours the reaction with high energy products, which may actually absorb heat. This may *reduce* the entropy of the *environment*, but the *increase* in the entropy of the *system* more than compensates.

Either way, the Gibbs free energy *always* decreases.

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