<P> Sublimations and vaporizations of the same substance have separate sets of Antoine coefficients, as do components in mixtures . Each parameter set for a specific compound is only applicable over a specified temperature range . Generally, temperature ranges are chosen to maintain the equation's accuracy of a few up to 8--10 percent . For many volatile substances, several different sets of parameters are available and used for different temperature ranges . The Antoine equation has poor accuracy with any single parameter set when used from a compound's melting point to its critical temperature . Accuracy is also usually poor when vapor pressure is under 10 Torr because of the limitations of the apparatus used to establish the Antoine parameter values . </P> <P> The Wagner Equation gives "one of the best" fits to experimental data but is quite complex . It expresses reduced vapor pressure as a function of reduced temperature . </P> <P> As a general trend, vapor pressures of liquids at ambient temperatures increase with decreasing boiling points . This is illustrated in the vapor pressure chart (see right) that shows graphs of the vapor pressures versus temperatures for a variety of liquids . At the normal boiling point of a liquid, the vapor pressure is equal to the standard atmospheric pressure defined as 1 atmosphere (760 Torr or 101 325 kPa). </P> <P> For example, at any given temperature, methyl chloride has the highest vapor pressure of any of the liquids in the chart . It also has the lowest normal boiling point (− 24.2 ° C), which is where the vapor pressure curve of methyl chloride (the blue line) intersects the horizontal pressure line of one atmosphere (atm) of absolute vapor pressure . </P>

The temperature at which the vapor pressure of a liquid is equal to 1 atm