Chemical reactions involve energy change.
During a chemical reaction, energy is transferred to or from the surroundings and the temperature changes.
For example, when we turn on the gas on our kitchen hob, a chemical reaction, called combustion or simply burning, takes place. Combustion transfers heat to its surroundings, so our food on top of it takes in the heat and cooks. The temperature in our cooking pot rises.
Reactions that transfer energy to their surroundings, like combustion, are exothermic reactions. Neutralisation is another type of exothermic reaction - this is the reaction between acids and alkalis.
The opposite happens in endothermic reactions. The energy in these reactions is taken from the surroundings.
Electrolysis and thermal decomposition are two types of endothermic reactions.
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