HAZMAT Technician Practice Exam

What physical change occurs at the boiling point of a substance?

1. A liquid becomes a gas

2. A solid becomes a gas

3. A solid becomes a liquid

4. A liquid becomes a solid

The correct answer is: A liquid becomes a gas

At the boiling point of a substance, the physical change that occurs is the transformation of a liquid into a gas. This process is known as boiling or vaporization, where the molecules in the liquid gain enough energy to break free from the intermolecular forces holding them together. When the temperature reaches the boiling point, the liquid's vapor pressure equals atmospheric pressure, leading to the formation of vapor bubbles within the liquid. Understanding this concept is crucial in various fields, including chemistry, materials science, and environmental science, as it applies to processes such as distillation, cooking, and the behavior of various substances under heat. This change is distinct from other phase changes, such as melting (solid to liquid) or sublimation (solid to gas), which occur at different temperatures and under different conditions.