What does vapor pressure measure?

Vapor pressure is defined as the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It measures the tendency of a substance to evaporate; that is, it quantifies how readily a substance transitions from a liquid state to a gaseous state. The higher the vapor pressure, the more volatile the substance, indicating that it has a greater capacity to evaporate.

Understanding vapor pressure is crucial in fields such as pesticide application, where knowing how quickly a substance can vaporize can impact its effectiveness and safety. Substances with high vapor pressures will evaporate more quickly, which can affect how they interact with the environment and target organisms. This information is vital for ensuring proper application methods and minimizing drift and volatility during aerial pesticide applications.

The other options do not accurately describe vapor pressure: viscosity relates to a liquid's resistance to flow, thickness refers to a liquid's physical dimension, and density measures mass per unit volume. None of these concepts directly relate to a substance's ability to evaporate, which is the core point of understanding vapor pressure.