What defines a chemical change?

A chemical change is characterized by a transformation that results in the formation of new materials with distinct properties that are different from those of the original substances. During a chemical change, bonds between atoms break and new bonds form, leading to the creation of different chemical substances. This process is not reversible by simple physical means, highlighting the depth of the transformation that has occurred.

In contrast, changes such as melting or freezing, which alter the state of a substance, do not create new materials; they simply change the physical form. Similarly, changes in size or shape, or temporary alterations, involve physical changes that do not involve alterations to the chemical structure of the substances. Therefore, the essence of a chemical change lies in the production of new materials, making the option that describes this aspect the correct choice.