Final answer:
A chemical change is the process where a pure substance's composition is altered, resulting in the formation of new substances with different properties, such as during combustion or corrosion. This transformation is a hallmark of a chemical reaction. Signs of such reactions can include heat, light, gas production, and color changes.
Step-by-step explanation:
The transformation of a pure substance that results in a change in its composition is known as a chemical change. Examples of such processes include combustion or corrosion, where the substance is converted into one or more different substances with altered compositions and properties. This transformation is indicative of a chemical reaction taking place.
During a chemical change, the substance demonstrates a chemical property by changing its molecular structure and forming new products. For instance, when a match burns, it undergoes a chemical change converting the substances in the match into different forms of matter with new physical properties such as heat, light, carbon dioxide, and water vapor.
Chemical reactions can be marked by signs such as heat or light production, gas evolution, color changes, or the formation of a precipitate. Such changes are essential in various fields, from scientific research to industrial applications, illustrating the resultant products of a reaction, which are depicted on the right side of the arrow in a chemical equation.