Heat energy can be given out or taken in from the surroundings during chemical reactions. The amount of energy transferred can be measured, this is called calorimetry.
When a chemical reaction occurs, energy is transferred to or from the surroundings. There is usually a temperature change. For example, when a bonfire burns it transfers heat energy to the surroundings. Objects near a bonfire become warmer. The temperature rise can be measured with a thermometer.
These are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. A thermometer is used to detect the temperature increase.
Some examples of exothermic reactions are:
These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become colder. A thermometer is used to detect the temperature decrease.
Some examples of endothermic reactions are:
The slideshow shows an exothermic reaction between sodium hydroxide and hydrochloric acid, and an endothermic reaction between sodium carbonate and ethanoic acid.