Chemistry Formulas

Vapor Pressure Formula

Table of Contents

When some liquid evaporates, the gaseous molecules are escaped from the air. If liquid is stored in a closed container then gaseous particles will not escape and it will be stored above the liquid. These evaporated particles will exert pressure over the liquid and this pressure is termed as the vapor pressure. At the same time, if some solid is dissolved in the liquid then a solution is created. The vapor pressure of the solution is lowered down by addition of solute.

\[\ P_{Solution} = X_{Solvent} \times PO_{Solvent} \]

In simple words, vapor pressure is defined as the pressure formed by the vapor in thermodynamics equilibrium at the condensed phases for a given temperature within a closed system. This is an indication of evaporation rate of liquid. It will tell you the tendency of particles to escape from the liquid.  Any substance at high vapor pressure rate and the normal temperature is termed as the volatile.

When the temperature of a liquid increases, it will increase the kinetic energy of molecules too. When the kinetic energy will increase, the number of molecules transitioning vapor will also increase, hence increasing the vapor pressure too. The pressure of vapor usually increases in a non-linear relationship and becomes equal to the atmospheric pressure soon.

When temperature become higher than the atmospheric pressure then vapor will convert to bubbles inside the bulk of substances. So, this is clear that temperature should always be higher for bubble transformation. In this way, calculating vapor pressure of solution is always easy with the help of a formula given above and you just have to put the values to find the final value.