Ch. 09: Liquids & Solids Vapor Pressure. Vapor = the gaseous state of a substance that has escaped...
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Transcript of Ch. 09: Liquids & Solids Vapor Pressure. Vapor = the gaseous state of a substance that has escaped...
Ch. 09: Liquids & SolidsVapor Pressure
Vapor Pressure• Vapor = the gaseous state of a substance that has escaped
from the liquid phase
e.g., ½-filled cup of coffee:
• vaporization = liquid is converted to its gas form
(in open system, it continues to complete evaporation)
liquid vapor
• dynamic equilibrium: rate vaporization = rate condensation
• vapor (a gas) follows gas laws
• this chapter on closed system: dynamic equilibrium between liquid & vapor.
Vapor Pressure
Vapor Pressure 9.1
• Theory:
• When temperature rises, the vapor pressure of a liquid increases. (molecules have sufficient energy to break away from the surface of the liquid)
• When the vapor pressure = pressure above the liquid, the liquid boils.
• Special case: @1 atm, bp is called the normal boiling Tb
Vapor Pressure 9.1
• Vapor pressure varies exponentially with temperature.
Clausius-Claperon equation:
or:
y = mx + b
Vapor Pressure 9.1
Clausius-Claperon equation:
@ T2: @ T1:
or
R = 8.31 J/mol-K
E.g., can find heat of vaporization; vapor pressures; temperature for specific vapor pressures
(similar equations)
• Clasius-Claperyon:Vapor Pressure
• Arrhenius:Temperature on Reaction Rate
• van’t HoffTemperature on Rate Constant
Vapor Pressure
Vp• = pressure exerted by the vapor over the liquid
• At equilibrium, Vp is independent of volume.
• The larger the volume, the more liquid that vaporizes
• ratio “n/V” remains constant, so:
• P = nRT/V does not change until all of the liquid has vaporized, and Vp will be less that Pequilibrium.
Vapor Pressure
Example 9.1A 2.0-L “cool mist” vaporizer adds moisture to dry air at 25oC. The room is 12’ x 12’ x 8’. VpH2O is 24 mmHg at 25oC. (Assume density of 1.00 g/mL)(a) If the vaporizer runs until it is empty, what is the vapor pressure of the water in the room?