Correct Answer: Ca(s) + 2H2O(ℓ) → Ca(OH)2(aq) + H2(g)
Reason:
A reaction (transmutation) is said to be spontaneous if it occurs on it's own, without any external stimulus. For spontaneous reaction, change in free energy (ΔG) is negative.
Among the given reactions, Ca(s) + 2H2O(ℓ) → Ca(OH)2(aq) + H2(g) occurs on its own with supplying external energy. Hence, it is a spontaneous reaction. Further, it is an exothermic reaction. So during the reaction heat is given out by the system.
On other hand, reaction: 2KClO3(s) → 2KCl(s) + 3O2(g) is a decompostion reaction. For occurrence of reaction, heat has to be supplied to system. Hence, this reaction is non-spontaneous in nature.
