What is meant by chemical change?

A chemical change refers to a process that transforms one or more substances into different substances through the breaking and forming of chemical bonds. This transformation involves significant modifications at the molecular level, meaning that the original substances will no longer retain their identity; they become entirely new chemical entities with distinct properties and compositions.

For instance, when iron reacts with oxygen to form rust (iron oxide), this is a clear illustration of a chemical change. The original elements (iron and oxygen) have undergone a transformation, resulting in a completely new substance that cannot simply return to its original components through physical methods, like boiling or freezing. This highlights the concept that chemical changes are typically irreversible under normal conditions.

Understanding this definition emphasizes the importance of bond alterations during chemical reactions, differentiating these changes from physical changes, which involve alterations in form or state without changing the substance's chemical identity.