Question

Enthalpy diagram for a particular reaction is given in Figure. Is it possible to decide spontaneity of a reaction from given diagram? Explain.

Answer 1

• It is not possible to make a decision on whether the given reaction will be spontaneous or not just by looking at its enthalpy diagram.

• From the given enthalpy diagram it can be said the change in enthalpy $\left(\Delta H\right)$ is positive for the reaction, i.e. it will be endothermic in nature.
• But when it comes to the spontaneity of a reaction, enthalpy change is just one factor and there are other important factors like entropy change and temperature, which decides the sign of gibbs free energy change and thus the spontaneity. $\Delta G=\Delta H–T\Delta S$
• Hence, enthalpy alone cannot determine the spontaneity of a reaction; one must have a look to the other contributing factors also.