HAZMAT Technician Practice Exam

What occurs at the freezing point of a substance?

1. A liquid changes into a solid

2. A solid becomes a liquid

3. A gas becomes a solid

4. A liquid becomes a gas

The correct answer is: A liquid changes into a solid

At the freezing point of a substance, a liquid transforms into a solid. This phase change occurs when the temperature drops to a specific point where the molecular motion of the liquid slows down enough for the molecules to arrange themselves into a solid structure. This process involves the release of energy, typically in the form of heat, which allows the solid state to form as the molecules become more tightly packed. In contrast, the other options describe different phase changes. The melting process, wherein a solid becomes a liquid, occurs as temperature rises above the freezing point. Sublimation refers to a gas turning directly into a solid, which is not related to the freezing point concept. Lastly, evaporation is the process where a liquid becomes a gas, which again is not pertinent to freezing. Thus, the correct understanding of the freezing point directly correlates with the transition of a liquid to a solid state, confirming that option A is indeed the accurate answer.