# How would you determine if a reaction is entropy driven or enthalpy driven?

Aug 18, 2017

We calculate entropy change, $\Delta S$, by standard summation.

#### Explanation:

$\Delta {S}^{\circ} \text{_"reaction}$ is given by.......

$\Sigma {S}^{\circ} \left\{\text{products"}-SigmaS^@{"reactants}\right\}$

And a similar summation gives you the enthalpy change. The single, unequivocal' criterion for the spontaneity of chemical change is give by $\Delta {G}^{\circ} = \Delta {H}^{\circ} - T \Delta {S}^{\circ}$.

$\Delta G$, the Gibbs free energy, can also be related to the thermodynamic equilibrium constant, i.e. $\Delta G = - R T \ln \left\{{K}_{\text{eq}}\right\}$.

And thus you need values for both enthalpy and entropy change for a given reaction. Most of the time entropy is the dominant term, but you need data for a given reaction.