Why is respiration considered as an exothermic process?

Respiration is considered an exothermic process because it involves the release of energy as heat. During respiration, cells in living organisms break down glucose (C6H12O6) and other nutrients to produce energy in the form of adenosine triphosphate (ATP), along with carbon dioxide (CO2) and water (H2O) as by-products. The overall process can be represented by the following simplified chemical equation for aerobic respiration:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Here, the energy released is mainly due to the oxidation of glucose, a process that involves transferring electrons from glucose to oxygen. This transfer is coupled to the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi), which cells then use to perform work, such as muscle contraction, active transport across membranes, and chemical synthesis.

Since the products of the reaction (CO2 and H2O) have lower energy than the reactants (glucose and oxygen), the difference in energy is released as heat. This is why respiration is exothermic—the energy content of the reactants is higher than that of the products, resulting in a net release of energy to the surroundings.

In contrast to photosynthesis, which is an endothermic process and requires an input of energy (usually from sunlight) to convert CO2 and H2O into glucose and O2, respiration releases the energy stored in glucose, thus being exothermic.