True Vapor Pressure corresponds to which concept?

• A. The actual vapor pressure
• B. The rate of evaporation
• C. The ambient pressure
• D. The external pressure

Answer: (A)

True vapor pressure is the actual pressure exerted by the vapor when it is in equilibrium with its liquid (or solid) at a specific temperature. It represents the vapor’s partial pressure inside a closed system and is a property of the substance at that temperature. It is not the rate of evaporation, which describes how fast molecules leave the surface, nor the ambient or external pressure surrounding the system (although external pressure can influence boiling when it matches the vapor pressure). In short, true vapor pressure is the actual vapor pressure the substance would exert under those conditions.