E

Exothermic Reaction

ΔH < 0 (heat released); H_products < H_reactants
Quick Reference
Formula / NotationΔH < 0 (heat released); H_products < H_reactants
Also Known AsHeat-releasing reaction, exothermal reaction, combustion (specific type)

What is Exothermic Reaction?

A chemical reaction that releases heat energy to the surroundings, causing the temperature to increase. The enthalpy change (ΔH) is negative. Examples include combustion, neutralization reactions, and many oxidation reactions. The products have lower energy than the reactants.

Formula & Notation

ΔH < 0 (heat released); H_products < H_reactants

Other Names / Synonyms: Heat-releasing reaction, exothermal reaction, combustion (specific type)

Properties & Characteristics

An exothermic reaction is one in which heat is released to the surroundings (ΔH < 0), causing the temperature of the surroundings (or the reaction mixture in an uninsulated system) to rise. Products have lower enthalpy than reactants. Examples: combustion (CH₄ + 2O₂ → CO₂ + 2H₂O, ΔH = −890 kJ/mol), neutralisation (H⁺ + OH⁻ → H₂O, ΔH = −57.1 kJ/mol), rusting of iron.

Uses & Applications

Exothermic reactions are exploited in: combustion engines and power stations (heat from combustion drives work), instant hot packs (CaCl₂ dissolving), hand warmers (iron oxidation), thermite welding (Fe₂O₃ + 2Al), and industrial reactors (Haber process ammonia synthesis is exothermic).

Safety Information

Highly exothermic reactions are fire and explosion hazards. Industrial scale-up requires heat management (cooling coils, reflux condensers, rate control by feed). Thermal runaway occurs when heat is generated faster than it can be removed. Reaction calorimetry and HAZOP analysis are mandatory before scale-up.

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

Key Facts

Term Exothermic Reaction
Formula ΔH < 0 (heat released); H_products < H_reactants
Synonyms Heat-releasing reaction, exothermal reaction, combustion (specific type)

Frequently Asked Questions

A chemical reaction that releases heat energy to the surroundings, causing the temperature to increase. The enthalpy change (ΔH) is negative. Examples include combustion, neutralization reactions, and many oxidation reactions. The products have lower energy than the reactants.

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