Water Vapor Pressure Calculator

Calculate the vapor pressure of water at any temperature using the Antoine equation.

Enter the temperature and get the vapor pressure of water in your preferred unit. Advanced users can customize Antoine constants.

Examples

See how to use the Water Vapor Pressure Calculator with real-world scenarios.

Standard Room Temperature (25°C)

Basic

Calculate the vapor pressure of water at 25°C in mmHg.

Temperature: 25 °C

Temperature Unit: C

Pressure Unit: mmHg

Boiling Point (100°C)

Basic

Find the vapor pressure of water at its boiling point (100°C) in kPa.

Temperature: 100 °C

Temperature Unit: C

Pressure Unit: kPa

Low Temperature (0°C)

Basic

Calculate the vapor pressure of water at 0°C in atm.

Temperature: 0 °C

Temperature Unit: C

Pressure Unit: atm

Custom Antoine Constants

Advanced

Use custom Antoine constants to calculate vapor pressure at 50°C in mmHg.

Temperature: 50 °C

Temperature Unit: C

Pressure Unit: mmHg

Antoine A: 8.14019

Antoine B: 1810.94

Antoine C: 244.485

Other Titles
Understanding Water Vapor Pressure Calculator: A Comprehensive Guide
Master the science and application of water vapor pressure calculations.

What is Water Vapor Pressure?

  • Definition and Physical Meaning
  • Importance in Chemistry and Engineering
  • Factors Affecting Vapor Pressure
Water vapor pressure is the pressure exerted by water vapor in equilibrium with its liquid phase at a given temperature. It is a key property in thermodynamics, meteorology, and chemical engineering.
Physical Meaning
At any temperature, some water molecules escape from the liquid to the vapor phase. The pressure these molecules exert is called vapor pressure.
Why is it Important?
Vapor pressure determines boiling point, evaporation rate, and is crucial in processes like distillation, weather prediction, and industrial drying.

Typical Values

  • At 25°C, the vapor pressure of water is about 23.8 mmHg.
  • At 100°C, the vapor pressure equals atmospheric pressure (760 mmHg).

Step-by-Step Guide to Using the Calculator

  • Inputting Temperature
  • Choosing Units
  • Advanced Options
Inputting Temperature
Enter the temperature in Celsius or Kelvin. The calculator automatically converts units as needed.
Choosing Output Units
Select your preferred pressure unit: mmHg, kPa, or atm. The result will be shown in all units for convenience.
Advanced: Custom Antoine Constants
Advanced users can enter custom Antoine constants for non-standard conditions or research purposes.

How-To Examples

  • Calculate vapor pressure at 50°C in kPa.
  • Use custom constants for a specific temperature range.

Real-World Applications of Water Vapor Pressure

  • Laboratory and Industrial Uses
  • Environmental Science
  • Everyday Life
Laboratory and Industrial Uses
Vapor pressure calculations are essential in chemical manufacturing, water treatment, and quality control.
Environmental Science
Understanding vapor pressure helps in weather forecasting, climate studies, and hydrology.
Everyday Life
Vapor pressure explains why water evaporates faster on hot days and why boiling point changes with altitude.

Applications

  • Predicting boiling point at high altitudes.
  • Designing efficient distillation processes.

Common Misconceptions and Correct Methods

  • Misunderstanding Temperature Effects
  • Incorrect Unit Conversions
  • Using Wrong Constants
Temperature Effects
Vapor pressure increases non-linearly with temperature. Doubling temperature does not double vapor pressure.
Unit Conversions
Always check your input and output units. The calculator helps by converting between mmHg, kPa, and atm.
Antoine Constants
Antoine constants are valid only within specific temperature ranges. Using the wrong set can lead to errors.

Mistakes to Avoid

  • Using Celsius instead of Kelvin in the formula.
  • Entering Antoine constants for ethanol instead of water.

Mathematical Derivation and Examples

  • Antoine Equation Explained
  • Clausius-Clapeyron Equation
  • Sample Calculations
Antoine Equation
The Antoine equation is an empirical relationship that relates vapor pressure and temperature: log10(P) = A - B / (C + T).
Clausius-Clapeyron Equation
For theoretical calculations, the Clausius-Clapeyron equation can be used, especially for phase change studies.
Sample Calculation
At 25°C, using A=8.07131, B=1730.63, C=233.426: log10(P) = 8.07131 - 1730.63 / (233.426 + 25) => P ≈ 23.8 mmHg.

Worked Examples

  • Calculate vapor pressure at 0°C, 25°C, and 100°C.
  • Compare results using different Antoine constants.