Vapor terminology: A vapor whose partial pressure is less than its saturation (equilibrium) vapor pressure at the same temperature is called a __________ vapor.

Introduction / Context:Precise terminology in phase equilibria helps avoid confusion in design of condensers, evaporators, and dryers. The relation between a vapor’s actual partial pressure and the saturation vapor pressure at the same temperature classifies the state as saturated, superheated, or supersaturated.

Given Data / Assumptions:

• Single-component vapor or a vapor in a gas mixture at temperature T.
• Saturation pressure p_sat(T) is the equilibrium vapor pressure at T.
• Partial pressure p_v of the vapor is known and p_v < p_sat(T).

Concept / Approach:When p_v = p_sat(T), the vapor is saturated and in equilibrium with its liquid. If p_v < p_sat(T) at the same temperature, the vapor has “excess temperature” relative to its saturation state: it is superheated. Supersaturated refers to a metastable state where p_v > p_sat(T) (or, equivalently, where relative humidity > 100% in gas–vapor mixtures), which is unstable and tends to condense upon nucleation.

Step-by-Step Solution:

Verification / Alternative check:On T–s or P–h diagrams, states to the right of the saturated vapor line at the same pressure are superheated; equivalently, at constant T, a vapor with lower pressure than saturation is superheated.

Why Other Options Are Wrong:

• Saturated: requires p_v = p_sat(T).
• Supersaturated: implies p_v > p_sat(T), the opposite case.
• Wet: indicates a mixture containing liquid droplets, not appropriate here.
• None of these: incorrect; the standard term is superheated.

Common Pitfalls:Confusing “supersaturated” with “superheated”; supersaturation is an overpressure (or overconcentration) state prone to condensation, whereas superheating is an underpressure state relative to saturation.

Final Answer:superheated