What is a common indicator of chemical change?

A common indicator of chemical change involves observable phenomena that indicate new substances have formed. The production of gas or a change in temperature are two significant indicators of a chemical reaction occurring.

When a gas is produced, such as during a reaction between vinegar and baking soda, it often manifests as bubbling or fizzing, which demonstrates that a new substance is forming. Similarly, a change in temperature — whether it be an increase (exothermic reaction) or a decrease (endothermic reaction) — signifies that energy is being absorbed or released, which is a hallmark of a chemical change. These indicators show that the original substances have undergone a transformation into different chemical entities with distinct properties.

In contrast, changes such as a simple alteration in color, shape, or volume may not necessarily indicate a chemical change. For example, color changes can occur during physical changes, and changes in shape or volume do not inherently imply that new substances have formed. Therefore, the production of gas or a change in temperature represents a more reliable evidence of a chemical change taking place.