# Vapor Pressure Calculator

Vapor pressure is the pressure exerted by a gas in equilibrium with its liquid form at a given temperature. It is an important property of liquids, as it provides a measure of the tendency of a liquid to evaporate. The vapor pressure of a liquid can be calculated using the Clausius-Clapeyron equation, which relates the vapor pressure of a liquid to its temperature and enthalpy of vaporization:

dP/dT = ΔHvap / T(dV/dT)

where dP/dT is the change in vapor pressure with temperature, ΔHvap is the enthalpy of vaporization, T is the temperature in kelvins, and dV/dT is the change in volume with temperature.

The enthalpy of vaporization can be determined experimentally or estimated from various models. Once the enthalpy of vaporization is known, the vapor pressure of a liquid can be calculated by integrating the Clausius-Clapeyron equation:

ln(P2/P1) = ΔHvap / R * (1/T1 - 1/T2)

where P1 and P2 are the vapor pressures at temperatures T1 and T2, respectively, and R is the ideal gas constant (8.31 J/molK).

The vapor pressure of a liquid can also be estimated using various empirical models, such as the Antoine equation, which provides a polynomial fit to experimental data:

log10(P) = A - B / (T + C)

where P is the vapor pressure, T is the temperature in kelvins, and A, B, and C are parameters that depend on the specific liquid.

Understanding the vapor pressure of a liquid is important in many applications, such as in determining the storage and transportation requirements for liquids, and in understanding the behavior of mixtures of liquids and gases.