WATER VAPOR PRESSURE CALCULATOR

What is Vapor Pressure? Vapor pressure is the pressure exerted by a liquid's vapor when the liquid and vapor are in dynamic equilibrium. This means the rate of molecules condensing into the liquid is equal to the rate of molecules evaporating into the vapor phase. Vapor pressure increases with temperature.

What is Saturation Vapor Pressure? This is the maximum amount of water vapor that can exist in the air at a particular temperature.

What is Partial Pressure? In a mixture of gases, the partial pressure is the pressure contributed by one specific gas in the mixture. The calculation of the partial pressure of water (i.e. water vapor pressure) is important because it is common to collect gases in inverted containers initially filled with water. In this scenario, the collected gas contains water molecules whose pressure is dependent on the temperature. The partial pressure of the collected gas is determined using Dalton's Law of Partial Pressures . . . .

P_Total = P_A + P_B + . . . .

When will I need to know the partial pressure of a gas in a mixture of gases? It is common to conduct gas-collecting lab experiments so that P_Total equals the atomospheric (barometric) pressure. If you were collecting oxygen gas by water displacement, Dalton's Law becomes . . . .

Atomospheric Pressure = P_O2 + P_H2O

. . . . and the Partial Pressure of O₂ is . . . .

P_O2 = Atomospheric Pressure - P_H2O

. . . . this P_O2 value can be used in the ideal gas equation (PV=nRT) . . . .

P_O2V_O2 = n_O2RT_O2

What is the relationship between water's partial pressure and its boiling point? The boiling point of water is the temperature at which its vapor pressure equals the surrounding atmospheric pressure.

Use the Water Vapor Pressure Calculator below to determine the vapor pressure of water at any temperature between 0°C and 100°C.