Respiration is a chemical change because it involves the breaking down of complex molecules (glucose) into simpler molecules (carbon dioxide and water), releasing energy in the process. Here's a breakdown:

* Reactants: Glucose (a complex sugar) and Oxygen are the reactants in respiration.

* Products: Carbon dioxide, water, and energy (in the form of ATP) are the products.

* Chemical Transformation: The bonds within glucose and oxygen molecules are broken, and new bonds are formed in carbon dioxide and water. This change in the arrangement of atoms signifies a chemical transformation.

Here's why this is considered a chemical change and not just a physical change:

* New substances are formed: Glucose and oxygen are transformed into entirely different substances, carbon dioxide and water.

* Energy is released: The process releases energy in the form of ATP, which is used by cells for various functions. This energy release is a clear indicator of a chemical reaction occurring.

* The change is irreversible: You can't simply reverse the process to get back glucose and oxygen from carbon dioxide and water.

In summary, respiration involves the breaking and forming of chemical bonds, resulting in new substances with different properties and energy release. This makes it a classic example of a chemical change.