An exothermic reaction releases energy into the environment. Some examples of these are:
- The combustion of carbon to form carbon dioxide. Heat is released in the process.
- Solidification of a liquid releases heat. This is one of the reasons why water does not get converted to ice spontaneously; the heat that is released has to be eliminated for the reaction to proceed. This is what happens in a refrigerator.
An endothermic reaction absorbs heat from the environment. Some examples of these are:
- The evaporation of a liquid is an endothermic reaction. If you place some alcohol on hand and let it evaporate you will find your hand feels cold.
- Photosynthesis is an endothermic reaction which requires energy that is obtained from sunlight.