Answer and Explanation:
At constant pressure and constant temperature, the Gibbs free energy of a process is given by the following equation:
ΔG= ΔH - T ΔS
The process is spontaneous when ΔG<0. For this, there are four alternatives depending on the signs of ΔH and ΔS and the temperature (T):
1) ΔH negative, ΔS positive ⇒ b)The reaction will be spontaneous at all temperatures.
ΔG= (-H) - T (+S) ⇒ ΔG<0 always
2) ΔH positive, ΔS negative ⇒ c)The reaction will be nonspontaneous at all temperatures.
ΔG= (+H) - T (-S) ⇒ ΔG>0 always
3) ΔH negative, ΔS negative ⇒ d)The reaction will be spontaneous at low temperature, but nonspontaneous at high temperature.
ΔG= (-H) - T (-S) ⇒ ΔG<0 if TΔS is lower than ΔH, because is the positive term
4)ΔH positive, ΔS positive ⇒ a)The reaction will be nonspontaneous at low temperature, but spontaneous at high temperature.
ΔG= (+H) - T (+S) ⇒ ΔG<0 if TΔS higher than ΔH because is the negative term
