Exothermic and Endothermic Reactions

Chemical reactions involve the transfer of energy, and this energy can either be given out or taken in. The energy transfer often occurs as heat energy, but it can also take other forms, such as light or sound.

Exothermic Reactions

Exothermic reactions release energy into the surroundings, leading to an increase in the surrounding temperature. Most reactions are exothermic.

There are red arrows, labelled "heat", leaving a conical flask to illustrate an exothermic reaction.

Some examples of exothermic reactions include:

  • Combustion reactions
  • Most neutralisation reactions
  • Most oxidation reactions

Hand warmers and self-heating cans of food use exothermic reactions to generate heat.

Endothermic Reactions

Endothermic reactions absorb energy from the surroundings, resulting in a decrease in the surrounding temperature.

A conical flask contains water and ice cubes, with red arrows going inwards labelled "heat", illustrating that heat is being absorbed.

Some examples of endothermic reactions include:

  • Electrolysis
  • Thermal decomposition – A compound breaks down into two or more substances.

Instant cold packs become very cold almost instantly by using endothermic reactions. They can be used to treat injuries.

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