Exothermic reaction
An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:
- reactants → products + energy
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Examples of exothermic reactions
- Combustion reactions of fuels
- Neutralization reactions such as direct reaction of acid and base
- Adding concentrated acid to water
- Burning of a substance
- Adding water to anhydrous copper(II) sulfate
- The thermite reaction
- Reactions taking place in a self-heating can based on lime and aluminum
- The setting of cement and concrete
- Many corrosion reactions such as oxidation of metals
- Most polymerisation reactions
- The Haber-Bosch process of ammonia production
Key points
- The concept and its opposite number endothermic relate to the enthalpy change in any process, not just chemical reactions.
- In endergonic reactions and exergonic reactions it is the sign of the Gibbs free energy that determines the equilibrium point, and not enthalpy. The related concepts endergonic and exergonic apply to all physical processes.
- the conceptually related endotherm and exotherm are concepts in animal physiology.
- In quantum numbers, when any excited energy level goes down to its original level for example: when n=4 fall to n=2, energy is released so, it is exothermic.
- Where an exothermic reaction causes heating of the reaction vessel which is not controlled, the rate of reaction can increase, in turn causing heat to be evolved even more quickly . This positive feedback situation is known as thermal runaway. An explosion can also result from the problem.
Measurement
Heat production or absorption in either a physical process or chemical reaction is measured using calorimetry. One common laboratory instrument is the reaction calorimeter, where the heat flow into or from the reaction vessel is monitored. The technique can be used to follow chemical reactions as well as physical processes such as crystallisation and dissolution.
See also
- Chemical thermodynamics
- Differential scanning calorimetry
- Endergonic
- Exergonic
- Endergonic reaction
- Exergonic reaction
- Exothermic
- Endothermic reaction
- Endotherm