How is the law of conservation of energy applied to chemical reactions?

The law of conservation of energy in chemical reactions states that energy cannot be created or destroyed, only transformed.

In the context of chemical reactions, the law of conservation of energy is often referred to as the first law of thermodynamics. This law states that the total amount of energy in a closed system remains constant. It can change from one form to another (such as potential energy to kinetic energy), but the total energy within the system is conserved.

In a chemical reaction, the energy needed to break the bonds in the reactants (the starting materials) is compared to the energy released when new bonds are formed in the products (the substances formed in the reaction). If the energy required to break the bonds is less than the energy released when new bonds are formed, the reaction is exothermic. This means it releases energy, usually in the form of heat. Combustion reactions, such as burning wood or petrol, are common examples of exothermic reactions.

On the other hand, if the energy required to break the bonds in the reactants is greater than the energy released when new bonds are formed, the reaction is endothermic. This means it absorbs energy from its surroundings, usually as heat. Photosynthesis in plants is a good example of an endothermic reaction.

In both exothermic and endothermic reactions, the total amount of energy remains the same before and after the reaction, in line with the law of conservation of energy. This is why in chemical equations, the energy is often included as a product or reactant to show that it is conserved. For example, in an exothermic reaction, the energy is shown as a product, while in an endothermic reaction, it is shown as a reactant.

In summary, the law of conservation of energy is a fundamental principle that governs all chemical reactions. It ensures that all energy involved in a reaction is accounted for, whether it is absorbed or released.