What is enthalpy change in a chemical reaction?

Enthalpy change in a chemical reaction is the amount of heat energy taken in or given out during a reaction.

Enthalpy change, often denoted by ΔH, is a fundamental concept in chemistry. It is a measure of the total energy of a thermodynamic system. In the context of a chemical reaction, the enthalpy change refers to the difference in energy between the reactants (the substances you start with) and the products (the substances you end up with).

If a reaction gives out heat to the surroundings, it is exothermic and the enthalpy change is negative. This is because the energy of the products is less than the energy of the reactants. Examples of exothermic reactions include combustion reactions, such as the burning of fuels, and many everyday reactions like rusting of iron.

On the other hand, if a reaction takes in heat from the surroundings, it is endothermic and the enthalpy change is positive. This is because the energy of the products is greater than the energy of the reactants. Examples of endothermic reactions include photosynthesis and the process of cooking an egg.

The enthalpy change of a reaction can be calculated if the enthalpies of formation of the reactants and products are known. It is usually expressed in kilojoules per mole (kJ/mol). Understanding enthalpy changes is crucial in chemistry as it helps us predict whether a reaction will occur spontaneously, and it also has important implications in industrial processes, where controlling the energy changes in reactions is vital.