Vapor Pressure

Vapor Pressure

Vapor Pressure


“What happens to water in a closed container?”

Liquids have many fascinating facets, and one of the fascinating facets about them is when put in a closed container, a gas will gradually form over time. What is this substance and how does it affect the surrounding environment? Well, let’s start by looking at it from a microscopic viewpoint. Well, first of all we know that molecules in a liquid move around in a semi-free fashion but are held together by cohesive forces resulting from intermolecular interaction. But what happens if the energy of one of these moving molecules overcomes such internal forces? As it turns out, this molecule will be freed from the constraints of the liquid substance and be allowed to float around as a gas. And if this liquid is trapped inside a closed container, then the gas molecules will be too. Some of these gas molecules will eventually lose kinetic energy and in turn will be dragged back into the liquid. Eventually, a steady state will be formed with the number of molecules leaving the liquid will equal the number returning to the liquid. As a result, this steady gas will exert a vapor pressure on the liquid beneath it.

Now here is where things become interesting. If one were to increase the temperature of the liquid, then then the kinetic energy of the molecules of the liquid will increase, causing a greater amount of liquid to be released into the gas, therefore increasing the vapor pressure of the gas!

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