ChemWhiz ReferenceGases & Liquids
Vapor Pressure of Water at Different Temperatures
Vapor pressure of liquid water from 0 °C to 100 °C in torr, kPa, and atm. Needed whenever a gas is collected over water: subtract the water vapor pressure from the total pressure (Dalton's law, P(gas) = P(total) − P(H2O)) before applying the ideal gas law.
01Use this when
Collecting a gas over water: P(dry gas) = P(total) − P(H2O) at the water temperature.
02Conditions
Liquid water, 0 °C to 100 °C.
03Watch out
Subtract the water vapor pressure at the ACTUAL temperature, not at 25 °C.
Vapor Pressure of Water, 0 to 100 °C
Water boils when its vapor pressure equals the external pressure; interpolate between rows as needed.
22 of 22
| 0 | 4.6 | 0.611 | 0.00603 |
| 4 | 6.1 | 0.814 | 0.00803 |
| 10 | 9.2 | 1.228 | 0.0121 |
| 15 | 12.8 | 1.706 | 0.0168 |
| 20 | 17.5 | 2.339 | 0.0231 |
| 22 | 19.8 | 2.645 | 0.0261 |
| 25 | 23.8 | 3.170 | 0.0313 |
| 30 | 31.9 | 4.247 | 0.0419 |
| 35 | 42.2 | 5.629 | 0.0556 |
| 40 | 55.4 | 7.384 | 0.0729 |
| 45 | 72.0 | 9.594 | 0.0947 |
| 50 | 92.6 | 12.4 | 0.122 |
| 55 | 118.2 | 15.8 | 0.156 |
| 60 | 149.6 | 19.9 | 0.197 |
| 65 | 187.8 | 25.0 | 0.247 |
| 70 | 234.0 | 31.2 | 0.308 |
| 75 | 289.5 | 38.6 | 0.381 |
| 80 | 355.6 | 47.4 | 0.468 |
| 85 | 434.0 | 57.9 | 0.571 |
| 90 | 526.4 | 70.2 | 0.693 |
| 95 | 634.6 | 84.6 | 0.835 |
| 100 | 760.0 | 101.3 | 1 |
Important Notes
- Water boils when its vapor pressure equals the external pressure (exactly 760 torr, 1 atm, at 100 °C), which is why the table ends there.
- Collecting a gas over water: the trapped gas is saturated with water vapor, so P(dry gas) = P(total) − P(H2O) at the collection temperature T. Look up P(H2O) at that temperature here.
- Vapor pressure grows roughly exponentially with temperature (Clausius-Clapeyron); interpolate between rows for intermediate temperatures.
- Values are computed from the IAPWS-IF97 saturation-pressure equation; the 100 °C entry is the defined normal boiling point (1 atm = 760 torr), which the equation itself places at 99.97 °C.
Verification references: Computed from the IAPWS-IF97 saturation-pressure equation (IAPWS Industrial Formulation 1997, Region 4).