Topic 15.4: Spontaneity

15.4.1 Predict whether a reaction or process will be spontaneous by using the sign of ΔG.

Gibb's free energy simply states whether a process would be spontaneous or not. So if ΔG is a negative, then the process will be spontaneous.

15.4.2 Calculate ΔG for a reaction using the equation ΔG = ΔH - TΔS and by using values of the standard free energy change of formation, ΔG

Use the information given to calculate the change in Gibb's free energy of formation. All of these values are performed at standard conditions.

15.4.3 Predict the effect of a change in temperature on the spontaneity of a reaction using standard entropy and enthalpy changes and the equation  ΔG = ΔH - TΔS

It is easy to instantly tell whether a reaction is spontaneous or not simply by looking at the positive and negative symbols. If enthalpy change is positive while entropy is negative, then the reaction is non-spontaneous and vice versa.