If the products and reactants have lower energy than the reactants, the reaction is not spontaneous. The reaction can also be spontaneous if the energy of the reactants and products is higher than the energy of the products. The energy of the transition state is greater than that of reactants or products.

The energy profile diagram shows the energy distribution of the system during reaction.

If the reaction produces less energy than the reactants, then the free energy of the reaction is less that zero [katex]\left( {\Delta {{\rm{G}}^o} < 0} \right)[/katex]

If the reaction occurs in an endothermic state, the reactants will have less energy than their products. In this case, the free energy of the reaction is greater that zero [katex]\left( {\Delta {{\rm{G}}^o} > 0} \right)[/katex]