Variation of equilibrium constant with temperature

The relationship can be shown by putting together two previously-mentioned equations:

This has the form of y = mx + c. So plotting lnK against (1/T) will give a slope with a gradient of (-ΔH° / R) and an intercept of (ΔS° / R).

Notice that whether the gradient is positive or negative depends on the sign of -ΔH°. So an exothermic reaction has K decrease with temperature, and an endothermic reaction has K increase with temperature.

Le Chatelier didn't know about equilibrium constants or these equations, but now we do, we are able to explain why he observed his principle consistently.