Chemical reactions transfer energy to, or from, the surroundings. They often cause a temperature change and it can be measured with a thermometer.

Exothermic reactions

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.

Endothermic reactions

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 get colder.

You can see an explanation here:

In the lab we have measured the transfer of energy of two chemical reactions:

- Exothermic reaction between NaOH and HCl.

- Endothermic reaction between Ba(OH)2 and NH4NO3.

Here are our experiments: