Dew point and saturation definitions:\nIf the partial pressure of the solvent vapor equals its saturation pressure at the same temperature, the system is at its ________.

Introduction / Context:
In gas–vapor systems (e.g., moist air), key temperatures define onset conditions of phase change at specified pressures or compositions. The two most common are the dew point and bubble point. Correctly identifying which condition is met by a given equality prevents misinterpretation in humidification, drying, and condenser design.

Given Data / Assumptions:

• Carrier gas with a condensable vapor (solvent).
• Equality p_v = p_sat(T) at the same temperature.
• Total pressure fixed.

Concept / Approach:
For a vapor–gas mixture, when the vapor’s partial pressure equals the saturation pressure at the mixture temperature, the vapor is just saturated and will begin to condense upon any further cooling. The temperature at which this occurs, for a fixed vapor partial pressure, is the dew point. Equivalently, that temperature is a saturation temperature for the vapor at that partial pressure. Hence, saying the system is at its dew point and at a saturation temperature are both correct descriptions of the same thermodynamic condition in this context.

Step-by-Step Solution:

Verification / Alternative check:
Psychrometric charts show the 100% relative humidity curve where p_v = p_sat(T); points along this curve are dew points for the corresponding vapor contents.

Why Other Options Are Wrong:

• Bubble point pertains to liquid mixtures where first bubble of vapor forms.
• Critical temperature is unrelated to this equality for mixtures at ordinary pressures.

Common Pitfalls:
Confusing dew point (vapor saturation in gas) with bubble point (boiling onset in liquid); overlooking that “saturation temperature” in mixtures is context-dependent.

Final Answer:
Both saturation temperature and dew point.