Thermodynamics vocabulary — vapor–liquid equilibrium:\nThe pressure at which a liquid and its vapor can coexist in equilibrium at a given temperature is called the __________ vapor pressure.

Introduction / Context:
In chemical engineering thermodynamics and phase equilibria, precise terminology is crucial. When a pure liquid and its vapor coexist without net evaporation or condensation at a fixed temperature, the system is at vapor–liquid equilibrium (VLE). The pressure of the vapor in equilibrium with its liquid at that temperature has a standard name that appears in phase diagrams, Antoine-equation correlations, and design of separation operations such as distillation and evaporation.

Given Data / Assumptions:

• Pure substance at a specified temperature.
• Liquid and vapor phases are present simultaneously, with no net mass transfer (equilibrium).
• No capillarity or curvature effects (bulk phases), and no noncondensable gases.

Concept / Approach:
For a pure component, the equilibrium pressure of the vapor above its liquid at temperature T is the saturated vapor pressure. This value increases monotonically with temperature and reaches the external pressure at the normal boiling point (when saturated vapor pressure equals 1 atm). In correlations such as the Antoine equation, log10 Psat is expressed as a function of 1/T, enabling engineers to estimate phase-change conditions and driving forces for mass transfer.

Step-by-Step Solution:
Identify the scenario: liquid and vapor in equilibrium at fixed T.The term used universally for the pressure of the vapor in equilibrium with its liquid is “saturated vapor pressure.”Therefore, the blank should be filled with “saturated.”

Verification / Alternative check:
At the normal boiling point, the saturated vapor pressure equals 1 atm; this is consistent with textbook definitions and phase diagrams where the liquid–vapor boundary (vapor pressure curve) is labeled Psat(T).

Why Other Options Are Wrong:
Limiting: not a standard term for VLE pressure.Real: ambiguous; all physical pressures are “real,” but the term does not denote equilibrium vapor pressure.Normal: “normal boiling point” is defined at 1 atm; “normal vapor pressure” is not a standard term.

Common Pitfalls:
Confusing saturated vapor pressure (equilibrium property at a given T) with partial pressure in a mixture, or with absolute/atmospheric pressure. Also, do not mix up “normal boiling point” (a temperature) with “vapor pressure” (a pressure).

Final Answer:
saturated