During endothermic reactions, energy is absorbed from the surrounding environment. The energy is typically transferred in the form of heat energy, and causes the reaction mixture and its environs to cool. A thermometer can be used to detect the decrease in temperature.
Examples of endothermic reactions include electrolysis, melting ice cubes, evaporation of water and the melting of solid salts. Exothermic reactions transfer heat energy to surrounding environments. The temperature change can also be detected using a thermometer. Common examples of exothermic reactions include burning, rusting iron, nuclear fission and neutralization reactions between alkalis and acids. Both endothermic and exothermic reactions cause differences in enthalpy, which is the total sum of kinetic and potential energies.