What is the relationship between enthalpy and entropy?

Apr 19, 2016

See below

Explanation:

Enthalpy ($H$) is defined as the amount of energy released or absorbed during a chemical reaction.

Entropy ($S$) defines the degree of randomness or disorder in a system.

Therefore, there is no direct relationship between entropy and enthalpy. However, the free energy ($G$) regroups both terms as:
$G = H - T S$

where at constant temperature, the change on free energy is defined as: $\Delta G = \Delta H - T \Delta S$.

Therefore, the free energy expression provides a relationship between enthalpy and entropy.

Thus, for a system at equilibrium, $\Delta G = 0$, and then we find that $\Delta S = \frac{\Delta H}{T}$.