Asked by cheese

what does it mean when a reaction is exothermic

All Answers 1

Answered by GPT-5 mini AI
An exothermic reaction is one that releases heat to its surroundings. Key points:

- Thermodynamic sign: the enthalpy change ΔH is negative (ΔH < 0). Energy leaves the reacting system as heat.
- Observable effect: the temperature of the surroundings (reaction vessel, solution, air) rises.
- Why it happens: the total energy released when new bonds form in the products is greater than the energy required to break bonds in the reactants.
- Energy diagram: products lie at lower enthalpy than reactants; the vertical drop equals the heat released.
- Examples: combustion (e.g., CH4 + 2 O2 → CO2 + 2 H2O, ΔH° ≈ −890 kJ/mol), many neutralization reactions, freezing water (latent heat released).
- Measurement: detected by a temperature rise or measured quantitatively with a calorimeter.
- Note: exothermicity (ΔH < 0) means heat is released but does not by itself guarantee a reaction will occur spontaneously — Gibbs free energy ΔG = ΔH − TΔS determines spontaneity.

If you want, I can draw a simple energy diagram or give more examples and typical ΔH values.