What is a chemical change?

A chemical change is correctly identified as a process that results in the formation of new chemical substances. During a chemical change, the original substances, known as reactants, undergo a transformation to create new products that have different properties from the reactants. This transformation typically involves the breaking and forming of chemical bonds, which alters the molecular structure of the substances involved.

For instance, when iron rusts, it reacts with oxygen to form iron oxide, which is a different substance with distinct characteristics compared to its initial components. This demonstrates the essence of a chemical change.

In contrast, physical changes involve alterations in form or appearance without changing the chemical composition, like mixing substances without a reaction or changing states (such as ice melting to water). A reversible reaction does not define all chemical changes, as some are irreversible, such as baking a cake. Similarly, combining physical changes does not capture the essence of a chemical change, as these changes do not lead to new substances being formed. Thus, the essence of a chemical change lies in the creation of new substances and the changes in chemical structure that occur during the process.