What is a chemical reaction?

A chemical reaction is a process in which substances interact, resulting in the formation of new substances with different chemical and physical properties compared to the original ones. This transformation often involves the breaking and forming of bonds between atoms, leading to a change in the composition of matter.

In the context of the other options, a change in physical properties refers to physical changes such as phase transitions (like melting or freezing), which do not involve a chemical transformation. The option suggesting that chemical reactions only occur under high-temperature conditions is too restrictive; many chemical reactions can and do occur at various temperatures. Similarly, stating that these reactions occur exclusively in living organisms overlooks the numerous chemical reactions that take place in inorganic contexts and everyday life, such as combustion, rusting, and reacting acids with bases. Thus, the essence of a chemical reaction is accurately captured in the explanation that involves substances combining and transforming into different substances.