National League for Nursing (NLN PAX) Practice Exam

In the context of chemical reactions, a change in color is often indicative of a chemical change. This occurs because chemical reactions involve the formation of new substances, which have different properties from the reactants, including their color. For example, when iron rusts, its color changes from metallic gray to reddish-brown due to the formation of iron oxide, a different substance with distinct characteristics. This alteration in color typically signifies that a chemical transformation has occurred at the molecular level.

A change in color does not usually occur during physical changes, where the substance remains the same despite alterations in state or appearance. Similarly, nuclear and electromagnetic changes involve different processes, such as alterations in atomic nuclei or changes in energy states, which do not inherently relate to color changes experienced in typical chemical reactions. Therefore, the identification of color change as a hallmark of chemical reactions is a cornerstone in understanding the nature of chemical changes.