A spontaneous reaction is energetically favorable compared to a non-spontaneous reaction because it releases free energy and moves to a more stable state.
A spontaneous reaction is one which releases free energy and moves to a more stable state. Instantaneous reactions occur rapidly with sudden release of energy. Therefore, a spontaneous reaction is energetically favorable compared to a non-spontaneous reaction, which does not release free energy and is not thermodynamically favored.
For example, the combustion of a piece of paper is a spontaneous reaction because it releases energy and moves to a more stable state. On the other hand, the reverse reaction of the combustion, where ash and smoke turn back into a piece of paper, is non-spontaneous as it requires an input of energy to proceed.