Examples for Exothermic and Endothermic Reactions

In an exothermic reaction, energy is released to the environment, in an endothermic reaction, energy is absorbed from the environment.

Examples of Exothermic Reactions

• Burning and Combustion Reactions: Gasoline in the car, coal on the grill, wood in the fireplace, heating with gas or oil - in all these chemical reactions, energy is released into the environment, the reaction is exothermic.
• Oxygen Gas Sample: Every pupil knows the so-called "oxyhydrogen gas sample", whereby the proof for hydrogen should be provided. The thereby occurring oxyhydrogen gas reaction is exothermic as one can easily recognize by the explosion.
• Gypsum: If dried gypsum (for example gypsum powder from the hardware store) is combined with water, heat is released.

Examples of Endothermic Reactions

• Decomposition of water into the components oxygen and hydrogen. For this reaction to work, we must constantly add external energy in the form of electrical current, otherwise the reaction will come to a standstill.
• Effervescent Powder in Water: When dissolving effervescent powder (citric acid + sodium bicarbonate) in water, the energy from the water is needed. This also makes the water colder.
• Lime Precipitation: The settling of lime on the walls of the kettle, of glasses or in the swimming pool is also an endothermic chemical reaction. The more energy added in the form of heat (turning on the water cooker), the better the reaction can proceed.

See the article about differences between exothermic and endothermic chemical reactions for more information.