Difference between Spontaneous and Non-Spontaneous Reactions

The main difference between spontaneous and non-spontaneous reactions is their thermodynamic favorability.

Spontaneous reactions are thermodynamically favorable, meaning they are exothermic reactions that can occur without any external input of energy. (Not all sponteneous reaction can occur without external energy, some of them might be endothermic)

Non-spontaneous reactions, on the other hand, are thermodynamically unfavorable, meaning they require an external input of energy to occur.

Also Read: Concept of Thermochemistry

Spontaneous vs. Non-Spontaneous Reactions

Here are the main difference between Spontaneous and Non-Spontaneous Reactions:

Characteristic	Spontaneous Reactions	Non-Spontaneous Reactions
Occurrence	Occur naturally	Require external energy input
Energy Change	Often exothermic (release energy)	Often endothermic (absorb energy)
Direction	Proceed toward a lower free energy state	Proceed toward a higher free energy state
External Influence	Typically do not require external energy	Require external energy source
Thermodynamic Favorability	Thermodynamically favorable	Thermodynamically unfavorable
Standard Conditions	Can occur under standard conditions	Often require non-standard conditions
Reversibility	Typically irreversible	Typically reversible
Reaction Rate	Tend to be rapid	Tend to be slow
Observable Signs	May show signs such as heat, gas bubbles, or a color change	May not show noticeable signs