Vapor Pressure Calculator

Antoine & Clausius-Clapeyron Equation Tool

Calculate the vapor pressure of common substances at any temperature using the Antoine or Clausius-Clapeyron equations. Supports multiple units and real-world chemistry applications.

Example Calculations

Try these sample calculations to see how the calculator works.

Water at 25°C (Antoine)

Antoine

Calculate the vapor pressure of water at 25°C using the Antoine equation.

Temperature (°C): 25 °C

First Temperature (°C): undefined °C

Second Temperature (°C): undefined °C

Vapor Pressure at T₁ (Pa): undefined Pa

Enthalpy of Vaporization (J/mol): undefined J/mol

Method: Antoine Equation

Substance: Water

Pressure Unit: mmHg

Ethanol at 60°C (Antoine)

Antoine

Calculate the vapor pressure of ethanol at 60°C using the Antoine equation.

Temperature (°C): 60 °C

First Temperature (°C): undefined °C

Second Temperature (°C): undefined °C

Vapor Pressure at T₁ (Pa): undefined Pa

Enthalpy of Vaporization (J/mol): undefined J/mol

Method: Antoine Equation

Substance: Ethanol

Pressure Unit: kPa

Water: Pressure at 80°C (Clapeyron)

Clapeyron

Given vapor pressure of water at 25°C (3168 Pa) and ΔHvap = 40650 J/mol, calculate vapor pressure at 80°C.

Temperature (°C): undefined °C

First Temperature (°C): 25 °C

Second Temperature (°C): 80 °C

Vapor Pressure at T₁ (Pa): 3168 Pa

Enthalpy of Vaporization (J/mol): 40650 J/mol

Method: Clausius-Clapeyron Equation

Substance: undefined

Pressure Unit: undefined

Acetone at 40°C (Antoine)

Antoine

Calculate the vapor pressure of acetone at 40°C using the Antoine equation.

Temperature (°C): 40 °C

First Temperature (°C): undefined °C

Second Temperature (°C): undefined °C

Vapor Pressure at T₁ (Pa): undefined Pa

Enthalpy of Vaporization (J/mol): undefined J/mol

Method: Antoine Equation

Substance: Acetone

Pressure Unit: bar

Other Titles
Understanding Vapor Pressure: A Comprehensive Guide
Master vapor pressure calculations for chemistry, engineering, and real-world applications.

What is Vapor Pressure?

  • Definition and Physical Meaning
  • Importance in Chemistry
  • Factors Affecting Vapor Pressure
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It is a fundamental property that determines how readily a substance evaporates.
Physical Meaning of Vapor Pressure
At equilibrium, the rate of evaporation equals the rate of condensation. The pressure at this point is the vapor pressure. Substances with high vapor pressure evaporate easily (volatile), while those with low vapor pressure are less volatile.
Factors Affecting Vapor Pressure
Temperature is the main factor: as temperature increases, vapor pressure rises exponentially. Intermolecular forces, molecular mass, and the presence of solutes also affect vapor pressure.

Vapor Pressure Examples

  • Water at 25°C: vapor pressure ≈ 23.8 mmHg
  • Ethanol at 60°C: vapor pressure ≈ 0.79 bar

Step-by-Step Guide to Using the Vapor Pressure Calculator

  • Select Calculation Method
  • Enter Required Data
  • Interpret Results
Our calculator supports two main methods: Antoine equation (for direct calculation using substance constants) and Clausius-Clapeyron equation (for estimating pressure at a new temperature given reference data and enthalpy of vaporization).
Using the Antoine Equation
Select the substance, enter the temperature, and choose the desired pressure unit. The calculator uses substance-specific Antoine constants to compute vapor pressure.
Using the Clausius-Clapeyron Equation
Enter the known vapor pressure (P₁) at temperature T₁, the new temperature T₂, and the enthalpy of vaporization (ΔHvap). The calculator estimates the vapor pressure at T₂.
Interpreting Results
Results are displayed in the selected unit. For Clausius-Clapeyron, the result is always in Pascals (Pa).

Step-by-Step Examples

  • Calculate water vapor pressure at 25°C using Antoine equation.
  • Estimate vapor pressure at 80°C given P₁ at 25°C and ΔHvap.

Real-World Applications of Vapor Pressure Calculations

  • Industrial Processes
  • Environmental Science
  • Everyday Life
Vapor pressure calculations are essential in chemical engineering, environmental science, meteorology, and product safety. They help design distillation columns, predict evaporation rates, and assess chemical hazards.
Industrial Applications
Used in distillation, solvent recovery, and process safety. Accurate vapor pressure data ensures efficient separation and safe storage of chemicals.
Environmental and Health Relevance
Vapor pressure affects air quality, pollutant dispersion, and the fate of chemicals in the environment. It is also crucial for understanding weather phenomena like humidity and cloud formation.
Everyday Examples
Boiling water, evaporation of perfumes, and drying of clothes all involve vapor pressure principles.

Application Examples

  • Designing a distillation column for ethanol-water separation.
  • Predicting evaporation rate of a solvent spill.

Common Misconceptions and Correct Methods

  • Unit Confusion
  • Temperature Range Errors
  • Equation Selection
Common mistakes include using the wrong units, applying equations outside their valid temperature range, or confusing Antoine and Clausius-Clapeyron methods.
Unit Consistency
Always check that input and output units are consistent. Antoine equation typically outputs in mmHg, but conversions are provided.
Temperature Range Validity
Each substance's Antoine constants are valid only within a specific temperature range. Using values outside this range leads to inaccurate results.
Choosing the Right Equation
Use Antoine for direct calculation with known constants. Use Clausius-Clapeyron when you have reference pressure, temperature, and enthalpy of vaporization.

Best Practice Guidelines

  • Don't use Antoine constants for water below 1°C or above 100°C.
  • Convert all pressures to Pa for Clausius-Clapeyron.

Mathematical Derivation and Examples

  • Antoine Equation
  • Clausius-Clapeyron Equation
  • Pressure Conversion
The Antoine equation is an empirical relationship: log₁₀(P) = A - B/(C+T), where P is vapor pressure (mmHg), T is temperature (°C), and A, B, C are substance-specific constants.
Clausius-Clapeyron Equation
The Clausius-Clapeyron equation relates vapor pressure at two temperatures: ln(P₂/P₁) = -ΔHvap/R (1/T₂ - 1/T₁), where P in Pa, T in Kelvin, ΔHvap in J/mol, and R is the gas constant (8.314 J/mol·K).
Pressure Unit Conversion
Common conversions: 1 atm = 101325 Pa = 1.01325 bar = 760 mmHg = 101.325 kPa. The calculator automatically converts between units as needed.

Calculation Examples

  • Calculate vapor pressure of acetone at 40°C using Antoine equation.
  • Estimate pressure at 80°C for water using Clausius-Clapeyron.