What are examples of exothermic and endothermic reactions?

Exothermic reactions include combustion and neutralisation, while endothermic reactions include photosynthesis and thermal decomposition.

Exothermic reactions are chemical reactions that release energy, usually in the form of heat. This means that the energy of the products is less than the energy of the reactants. A common example of an exothermic reaction is combustion, such as the burning of wood or petrol. In these reactions, the fuel reacts with oxygen to produce carbon dioxide, water, and a large amount of heat. Another example is neutralisation, which is the reaction between an acid and a base. This reaction produces a salt and water, and also releases heat. For instance, when hydrochloric acid reacts with sodium hydroxide, the resulting solution is warmer than the original reactants.

On the other hand, endothermic reactions are chemical reactions that absorb energy from their surroundings, usually also in the form of heat. This means that the energy of the products is greater than the energy of the reactants. A well-known example of an endothermic reaction is photosynthesis, the process by which green plants convert carbon dioxide and water into glucose and oxygen, using sunlight as an energy source. Another example is thermal decomposition, which is the breaking down of a compound using heat. For instance, when heating calcium carbonate, it decomposes into calcium oxide and carbon dioxide, and this process absorbs heat from the surroundings.

Understanding these reactions and their energy changes is crucial in chemistry. It helps us predict whether a reaction will occur spontaneously or not, and it also has practical applications in various fields, such as energy production, cooking, and even in our own bodies.