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Spontaneous Reaction

ΔG < 0 for spontaneous; ΔG = ΔH - TΔS
Quick Reference
Formula / NotationΔG < 0 for spontaneous; ΔG = ΔH - TΔS
Also Known AsThermodynamically favourable reaction, exergonic reaction, downhill reaction

What is Spontaneous Reaction?

A reaction that proceeds in a given direction without requiring continuous external energy input under specified conditions. Spontaneity is determined by the sign of ΔG: negative ΔG means spontaneous. Spontaneous does not mean fast — diamonds converting to graphite is spontaneous but extremely slow.

Formula & Notation

ΔG < 0 for spontaneous; ΔG = ΔH - TΔS

Other Names / Synonyms: Thermodynamically favourable reaction, exergonic reaction, downhill reaction

Properties & Characteristics

A spontaneous reaction is one that proceeds without external input of energy, driven by a decrease in Gibbs free energy (ΔG < 0). Spontaneity depends on both the enthalpy change and entropy change of the system and surroundings. A reaction can be spontaneous at some temperatures but not others depending on the signs of ΔH and ΔS. Spontaneous does not imply fast — the reaction may have a high activation energy.

Uses & Applications

The concept of spontaneous reactions guides industrial process design, identifying which reactions can be driven without excessive energy input. In biochemistry, spontaneous reactions (ΔG < 0) drive metabolic pathways. Battery operation relies on spontaneous redox reactions to generate electrical energy.

Safety Information

Spontaneous exothermic reactions may be hazardous if uncontrolled, releasing heat rapidly. Understanding spontaneity helps assess the risk of runaway reactions in chemical processes.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Spontaneous Reaction
Formula ΔG < 0 for spontaneous; ΔG = ΔH - TΔS
Synonyms Thermodynamically favourable reaction, exergonic reaction, downhill reaction

Frequently Asked Questions

A reaction that proceeds in a given direction without requiring continuous external energy input under specified conditions. Spontaneity is determined by the sign of ΔG: negative ΔG means spontaneous. Spontaneous does not mean fast — diamonds converting to graphite is spontaneous but extremely slow.

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