Thermodynamics and Thermochemistry
19.0 Enthalpy, Entropy, Free Energy Changes and The Nature of Process
19.0 Enthalpy, Entropy, Free Energy Changes and The Nature of Process
| $\Delta H$ | $\Delta S$ | $\Delta G = \Delta H - T\Delta S$ | Remarks |
| $-$ | $(+)$ | $(–)$ always | Spontaneous |
| $+$ | $+$ | $(+)$ at low temperature $(–)$ at high temperature | Non spontaneous Spontaneous |
| $-$ | $-$ | $(–)$ at high temperature $(+)$ at low temperature | Spontaneous Non spontaneous |
$?G°$ is related to equilibrium constant by expression
$$\Delta G^\circ = - RT\;lnK$$
$$\Delta G^\circ = - 2.303\;RT\;logK$$
Here $\Delta G^\circ = $ Change in standard free energy
Standard free energy change is change in free energy when all the reactants and products are at unit concentration $\left( {for\;{K_C}} \right)$ or at the unit pressure $\left( {for\;{K_P}} \right)$
$K=$ equilibrium constant for reversible reaction
