# what is vapor pressure?

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Most liquids are volatile to some degree and go to the vapor state. Suppose a liquid is placed in a container. Some of the liquid will vaporize and remain in the vapor state in the closed container. Eventually the vapor and the liquid will reach equilibrium. Suppose you had a pressure gauge attached to the container. The gauge would indicate the total pressure of the gases in the container. Subtracting out whatever pressure there was before the introduction of the liquid, you would get the pressure of the vapor of the liquid. Usually, the vapor pressure will vary with the temperature of the liquid. As the liquid temperature increases, the vapor pressure will also increase.

Often we collect gases "over water" as the gas bubbles up through water in an inverted flask or bottle and displaces the water. Despite that, there is still water vapor in the container. The pressure of the gas being collected is the total pressure less the vapor pressure of water at that temperature. The vapor pressure of water can be read from a chart of pressure vs temperature.

• Anonymous

A measure of a substance's propensity to evaporate, vapor pressure is the force per unit area exerted by vapor in an equilibrium state with surroundings at a given pressure. It increases exponentially with an increase in temperature. A relative measure of chemical volatility, vapor pressure is used to calculate water partition coefficients and volatilization rate constants.

by the way thnkz for the 2 points

• A measure of a substance's propensity to evaporate, vapor pressure is the force per unit area exerted by vapor in an equilibrium state with surroundings at a given pressure. It increases exponentially with an increase in temperature. A relative measure of chemical volatility, vapor pressure is used to calculate water partition coefficients and volatilization rate constants.

• In a general sense, it is the pressure that one can measure of the vapor phase, the gas phase. Vapor pressure is normally the portion of the total gas phase pressure that is caused by the substance under discussion

More specifically, it is a way of measuring or quantifying the chemical activity of a solid or liquid in contact with a gas. All substances lose some of their molecules at the contact zone, as vibrations in the solid or liquid kick off the random molecules into the gas phase. At the same time, some of those molecules in the gas phase will return to the solid or liquid.

The presence of these molecules in the gas phase provides some work energy that adds to the measurable pressure of the gas phase. .