Grade 10 Science Practice Exam 2026 - Free Science Exam Practice Questions and Study Guide

A change in color is a common indicator of a chemical change because it often signifies that a new substance has been formed during the reaction. For instance, when iron rusts, it changes color from shiny metallic gray to reddish-brown, indicating that it has reacted with oxygen and moisture in the air to create iron oxide. This is not simply a physical change, where the form of the material changes but the substance remains the same; here, the formation of a completely different substance is the key factor.

While changes in texture, size, and volume can occur during physical changes, they do not necessarily indicate that a chemical reaction has taken place. Therefore, observing a change in color is one of the most reliable indicators of a chemical change occurring.