How To Find Vapor Pressure Of Ethanol

Vapor Pressure level

The Macroscopic View

The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid (or solid); that is, the pressure of the vapor resulting from evaporation of a liquid (or solid) higher up a sample of the liquid (or solid) in a airtight container. Examples:

substance	vapor pressure at 25^oC
diethyl ether	0.7 atm
bromine	0.3 atm
ethyl booze	0.08 atm
water	0.03 atm

The vapor pressure of a liquid varies with its temperature, as the following graph shows for water. The line on the graph shows the boiling temperature for water.

Graph of vapor pressure vs temperature for water

As the temperature of a liquid or solid increases its vapor pressure also increases. Conversely, vapor pressure decreases equally the temperature decreases.

The vapor pressure of a liquid can be measured in a diversity of ways. A simple measurement involves injecting a little of the liquid into a closed flask connected to a manometer. Click here for an illustration.

The Microscopic View

When a solid or a liquid evaporates to a gas in a airtight container, the molecules cannot escape.
Some of the gas molecules will somewhen strike the condensed phase and condense back into it.
When the rate of condensation of the gas becomes equal to the rate of evaporation of the liquid or solid, the amount of gas, liquid and/or solid no longer changes.
The gas in the container is in equilibrium with the liquid or solid.

The pressure exerted by the gas in equilibrium with a solid or liquid in a closed container at a given temperature is chosen the vapor pressure level.

Factors That Touch Vapor Pressure

Surface Area : the surface area of the solid or liquid in contact with the gas has no event on the vapor pressure.

Types of Molecules : the types of molecules that brand up a solid or liquid determine its vapor pressure. If the intermolecular forces between molecules are:

relatively potent, the vapor pressure level will exist relatively low.
relatively weak, the vapor pressure volition exist relatively loftier.

= C

= O

= H

ethyl ether (C₄H₁₀O)
P_vapor (25^oC) = 520 torr
The relatively weak dipole-dipole forces and London dispersion forces betwixt molecules results in a much higher vapor pressure compared to ethyl alcohol.

ethyl booze (C₂H₆O)
P_vapor (25^oC) = 75 torr
Although dipole-dipole forces and London dispersion forces also exist betwixt ethyl booze molecules, the strong hydrogen bonding interactions are responsible for the much lower vapor pressure compared to ethyl ether.

Temperature : at a higher temperature, more molecules have plenty energy to escape from the liquid or solid. At a lower temperature, fewer molecules have sufficient energy to escape from the liquid or solid.