What is Vapor Pressure?

Vapor pressure is a fundamental thermodynamic property defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. Essentially, it indicates the evaporation rate of a liquid. Substances with a high vapor pressure at normal temperatures are often referred to as volatile.

How to Use This Vapor Pressure Calculator

Using our online tool is simple and accurate. First, select a common substance from the dropdown menu (such as Water, Ethanol, or Acetone). If you have specific data for a different chemical, select "Custom" and enter the Antoine constants (A, B, and C). Input the temperature and specify the unit (Celsius or Kelvin). Click "Calculate" to instantly see the results in mmHg, kPa, atm, and psi.

The Antoine Equation Explained

This calculator primarily uses the Antoine Equation, which is a mathematical expression relating the vapor pressure and temperature for pure components. The formula is expressed as:

log₁₀(P) = A - (B / (T + C))

Where P is the vapor pressure, T is the temperature, and A, B, C are substance-specific coefficients. It is the most widely used empirical correlation for vapor pressure in engineering and chemistry.

Frequently Asked Questions

Why does vapor pressure increase with temperature?

As temperature increases, the kinetic energy of the molecules in a liquid also increases. More molecules gain enough energy to escape the liquid surface and enter the gas phase, thereby increasing the pressure exerted by the vapor.

What is the boiling point in terms of vapor pressure?

The boiling point of a liquid is the temperature at which its vapor pressure equals the external atmospheric pressure surrounding the liquid.

What are Antoine constants?

Antoine constants are empirically derived parameters specific to a chemical substance and a specific temperature range. They are derived from experimental data to ensure high accuracy within that range.