Exothermic reactions
These are reactions that transfer energy to the surroundings (ie the energy exits from the reaction, hence the name exothermic). 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.
Examples:
Combustion
Neutralisation between acids and alkali
Endothermic reactions
These are reactions that take in energy from the surroundings (ie energy enters the reaction, which will help you to remember the name endothermic). 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.
Example:
Electrolysis