HAZMAT Technician Practice Exam

What characterizes a physical change?

1. A change in the chemical properties of a substance

2. A process that alters a substance's physical form without changing its chemical properties

3. The formation of a new chemical compound

4. The release of energy during a chemical reaction

The correct answer is: A process that alters a substance's physical form without changing its chemical properties

A physical change is characterized by a process that alters a substance's physical form while keeping its chemical properties intact. This means that the substance itself does not undergo any transformation at the molecular level; instead, it may change in state (such as from solid to liquid), in size, shape, or appearance. For instance, when ice melts to become water, the water's chemical composition remains H2O, even though its state has transitioned from solid to liquid. Focusing on the other options helps clarify why they do not fit the definition of a physical change. A change in the chemical properties of a substance implies a modification at the molecular or atomic level, which aligns more with a chemical change rather than a physical one. Similarly, the formation of a new chemical compound and the release of energy during a chemical reaction indicate chemical processes, where the original substances are transformed into entirely different entities. Thus, only the process that alters a substance's form without affecting its chemical makeup qualifies as a physical change.