Ontario Grade 9 Destreamed Science (SNC1W1) 2026 Practice Exam

The production of gas during a reaction is a strong indicator of a chemical change occurring within the substances involved. In a chemical reaction, bonds between atoms are broken and formed, leading to the creation of new substances with different properties. The generation of gas is often a hallmark of such transformations, which might happen through processes like the reaction of an acid with a carbonate or during combustion.

In contrast, physical changes involve alterations in the state or appearance of a substance without changing its chemical composition. Examples include changes in phase such as melting, boiling, or dissolving. Mass change is not a recognized type of change that describes the process involved; it typically refers to the conservation of mass principle in reactions. Temperature change can occur during both physical and chemical changes and does not specifically indicate that a chemical reaction has taken place. Thus, the presence of gas production serves as a clear marker of a chemical change, making it the appropriate choice in this context.