HAZMAT Technician Practice Exam

What does vapor pressure indicate?

1. The pressure of a gas compared to the atmosphere

2. The pressure exerted by a vapor over a liquid

3. The pressure needed to keep a liquid from evaporating

4. The pressure of a liquid at boiling point

The correct answer is: The pressure exerted by a vapor over a liquid

Vapor pressure is a critical concept in understanding how substances behave when they are in a liquid and gaseous state. It specifically refers to the pressure exerted by the vapor present in a container over a liquid when the system is in equilibrium. In simpler terms, it measures how much vapor is present above the liquid and the tendency of the liquid to evaporate into the vapor phase. When a liquid is in a closed environment, molecules at the surface escape into the air as they gain enough energy to overcome intermolecular forces. This escaping process leads to the formation of vapor, and the pressure that this vapor exerts above the liquid reaches a point where it equals the pressure exerted by the liquid’s surface. This is what is quantified as vapor pressure. Understanding vapor pressure is vital in hazardous materials management because it helps determine how volatile a substance is and its potential to release harmful vapors into the atmosphere. Substances with high vapor pressures readily evaporate and can contribute to hazardous conditions, while those with low vapor pressures tend to remain liquid. Options related to the other choices do not capture the essence of vapor pressure accurately. For example, the pressure of a gas compared to the atmosphere focuses on a broader context that doesn't specifically address the relationship with a liquid.