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Difference between Spontaneous and Non-Spontaneous Reactions

October 11, 2023
written by Adeel abbas

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.

image showing Difference between Spontaneous and Non-Spontaneous Reactions

Also Read: Concept of Thermochemistry

Spontaneous vs. Non-Spontaneous Reactions

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

CharacteristicSpontaneous ReactionsNon-Spontaneous Reactions
OccurrenceOccur naturallyRequire external energy input
Energy ChangeOften exothermic (release energy)Often endothermic (absorb energy)
DirectionProceed toward a lower free energy stateProceed toward a higher free energy state
External InfluenceTypically do not require external energyRequire external energy source
Thermodynamic FavorabilityThermodynamically favorableThermodynamically unfavorable
Standard ConditionsCan occur under standard conditionsOften require non-standard conditions
ReversibilityTypically irreversibleTypically reversible
Reaction RateTend to be rapidTend to be slow
Observable SignsMay show signs such as heat, gas bubbles, or a color changeMay not show noticeable signs