The Dew Point The vapor pressure of water (see Problem 18.88) decreases as the temperature decreases. If the amount of water vapor in the air is kept constant as the air is cooled, a temperature is reached, called the dew point, at which the partial pressure and vapor pressure coincide and the vapor is saturated. If the air is cooled further, vapor condenses to liquid until the partial pressure again equals the vapor pressure at that temperature. The temperature in a room is 30.0°C. A meteorologist cools a metal can by gradually adding cold water. When the can temperature reaches 16.0°C, water droplets form on its outside surface.
What is the relative humidity of the 30.00C air in the room? The table lists the vapor pressure of water at various temperatures:

Temperature (C) Vapor Pressure (Pa) 1.23 X 10 1.40 10 1.60 10 1.81 10 2.06 10 2.34 10 2.65 10 2.99 x 10 3.36 x 10 3.78 X 10 4.25 x 10 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0