Certified Safety Professional Practice Exam

Vapor pressure refers to the pressure exerted by vapor molecules that are in equilibrium with their liquid phase above the surface of a liquid in a closed container. As some of the molecules of a liquid escape from the surface and enter the gas phase, they exert pressure. This vapor pressure is an important property because it indicates the tendency of a liquid to evaporate; higher vapor pressures mean that the liquid can evaporate more readily. Vapor pressure varies with temperature, and it plays a crucial role in various applications, including distillation, boiling, and understanding the behavior of volatile substances.

In this context, the other options do not accurately describe vapor pressure. The weight of the liquid in a sealed container pertains to mass, not pressure. The temperature at which a liquid ignites relates to its flammability, not its vapor behavior. Lastly, measuring air quality around a liquid focuses on contaminants or air pollutants, rather than the physical properties of the liquid itself.