What indicates a chemical change has occurred?

A chemical change is characterized by a transformation that results in the formation of new substances with different properties from the original substances. The presence of indicators such as the formation of a gas, a change in color, or the creation of a precipitate strongly suggest that a chemical reaction has taken place. For instance, when vinegar reacts with baking soda, the production of carbon dioxide gas (bubble formation), an observable color shift, or the creation of a solid precipitate are clear signs of chemical changes.

In contrast, while a change in the state of matter or a temperature change can also occur during physical or chemical changes, they do not exclusively indicate a chemical change. Similarly, a change in size typically pertains to physical changes rather than reflecting the creation of new chemical substances. Thus, the presence of gas formation, color change, or precipitate effectively signifies a chemical transformation.