A liquid will evaporate if it is at a temperature where its vapor pressure is greater than the surrounding air. The vapor pressure of a liquid is affected by temperature and ambient pressure, with higher temperatures leading to higher vapor pressures. In this article, we’ll look at how to calculate the vapor pressure of an ideal gas and apply that knowledge in order to predict which liquids will evaporate under certain conditions (such as when placed on a hot surface).

What is vapor pressure?

Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phases at a given temperature. The equilibrium vapor pressure of substances is an intrinsic property that is independent of the presence or absence of liquid. It depends only on the composition, temperature, and any impurities in the substance.

The pressure exerted by a saturated liquid (at its boiling point) is known as saturation vapor pressure and it increases with an increase in temperature until all molecules escape from the solution as gas, thus drying out the liquid completely and producing an unsaturated vapor state.

If you want to learn more about the vapor pressure of water you can check out our Vapor Pressure of Water Calculator.

Clausius-Clapeyron equation

A vapor pressure chart is a graphical representation of the Clausius-Clapeyron equation, which is used to calculate the vapor pressure of a liquid. The Clausius-Clapeyron equation was developed by German physicist Rudolf Clausius and French mathematician Benoît Paul Émile Clapeyron in 1850.

In its simplest form, the Clausius-Clapeyron equation states that for every degree Celsius increase in temperature, a given amount (usually one atmosphere) added to its pressure will cause an additional drop in temperature. This means that if you know how much gas or liquid can be dissolved into another substance at one atmosphere and given temperature, then you also know how much it would expand as you raise it closer to room temperature—and vice versa!

The main reason this rule is so important? It helps us understand how different things react during combustion processes like explosions or being lit on fire…

What is the enthalpy of vaporization?

Now that you know what the vapor pressure is, let’s look at the enthalpy of vaporization. The enthalpy of vaporization is the enthalpy change when a substance changes from its liquid phase to its gaseous state (i.e., boiling). This can also be referred to as heat of vaporization or heat required to convert 1 mole of a substance from the liquid phase to its gaseous state.

Clausius-Clapeyron equation

The Clausius-Clapeyron equation is a thermodynamic relationship that predicts the vapor pressure of water at different temperatures. This can be useful for determining what the vapor pressure of a substance will be at any given temperature, which can then be used to determine its dew point.


What determines vapor pressure?

Three common factors that influence vapor press are surface area, intermolecular forces, and temperature.

What does a high vapor pressure mean?

The vapor pressure of a liquid lowers the amount of pressure exerted on the liquid by the atmosphere. As a result, liquids with high vapor pressures have lower boiling points.

Does humidity affect vapor pressure?

As the saturation vapor pressure increases with rising temperature, the relative humidity decreases when the vapor pressure is constant.