Evaporation H2O(g) molecules (water vapor) H2O(l)
Evaporation H2O(g) molecules (water vapor) H2O(l) molecules
Evaporation H2O(g) molecules (water vapor) H2O(l) molecules
How Vapor Pressure is Measured 760 mm + 120 mm = 880 mm Hg 1 atm = 760 mm Hg Animation by Raymond Chang All rights reserved
Manometer Atmospheric Pressure Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
Manometer A 760 mm Hg BIG = small + height 760 mm 120 mm Small = 640 mm Hg h = 120 mm ? Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
Manometer B 760 mm Hg BIG = small + height 760 mm 120 mm BIG = 880 mm Hg h = 120 mm ? Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
The Manometer and Vapor Pressure
Barometer & Manometer atmospheric pressure = 101.3 kPa 750 mm confined gas confined gas confined gas 600 mm 500 mm 325 mm 200 mm 150 mm 100 mm (a) (b) (c) (d)
Pressure and Temperature STP (Standard Temperature and Pressure) standard temperature standard pressure 0oC 1 atm 273 K 101.3 kPa 760 mm Hg Equations / Conversion Factors: K = oC + 273 oC = K – 273 1 atm = 101.3 kPa = 760 mm Hg
Convert 25oC to Kelvin. K = oC + 273 25oC + 273 = 298 K How many kPa is 1.37 atm? 101.3 kPa X kPa = 1.37 atm = 138.8 kPa 1 atm How many mm Hg is 231.5 kPa? 760 mm Hg X mm Hg = 231.5 kPa = 1737 mm Hg 101.3 kPa
Pa higher pressure manometer: measures the pressure of a confined gas AIR PRESSURE higher pressure CONFINED GAS Pa Hg HEIGHT DIFFERENCE manometer: measures the pressure of a confined gas
Atmospheric pressure is 96.5 kPa; mercury height difference is 233 mm. small Atmospheric pressure is 96.5 kPa; 96.5 kPa mercury height difference is 233 mm. Find confined gas pressure, in atm. BIG 1.26 atm X atm SMALL + HEIGHT = BIG 233 mm Hg 96.5 kPa + 233 mm Hg = X atm 1 atm 1 atm 96.5 kPa + 233 mm Hg = X atm 101.3 kPa 760 mm Hg 0.953 atm + 0.307 atm = X atm X = 1.26 atm
Vapor Pressure measure of the tendency for liquid particles to enter gas phase at a given temp. a measure of “stickiness” of liquid particles to each other more “sticky” less likely to vaporize In general: LOW v.p. not very more likely to HIGH v.p. NOT all liquids have same v.p. at same temp.
Volatile substances evaporate easily (have high v.p.’s). 100 80 CHLOROFORM PRESSURE (kPa) 60 ETHANOL b.p. = 78oC 40 20 WATER b.p. = 100oC 20 40 60 80 100 TEMPERATURE (oC) Volatile substances evaporate easily (have high v.p.’s). BOILING when vapor pressure = confining pressure (usually from atmosphere) atmospheric pressure is 101.3 kPa
Vapor Pressure Pressure (KPa) Temperature (oC) 61.3oC 78.4oC 100oC 101.3 93.3 80.0 66.6 chloroform ethyl alcohol Pressure (KPa) 53.3 40.0 water 26.7 13.3 10 20 30 40 50 60 70 80 90 100 Temperature (oC)
BOILING when vapor pressure = confining pressure (usually from atmosphere) At sea level and 20oC… ETHANOL WATER AIR PRESSURE (~100 kPa) VAPOR PRESSURE (~5 kPa) (~10 kPa)
ETHANOL WATER NET PRESSURE (~95 kPa) (~90 kPa)
Water Molecules in Liquid and Steam
Microscopic view of a liquid near its surface The high energy molecules escape the surface.
Behavior of a liquid in a closed container
Water rapidly boiling on a stove
Pressure Cooker http://gotethnicfoods.com/pictures/Regular/AGLS020.jpg Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.
120oC https://www.storesonlinepro.com/files/1730690/uploaded/Presto%2001755%20Pressure%20Cooker%20Canner.jpg
Formation of a bubble is opposed by the pressure of the atmosphere Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 452
Vapor Pressure Pressure (KPa) Temperature (oC) 61.3oC 78.4oC 100oC 101.3 93.3 80.0 66.6 chloroform ethyl alcohol Pressure (KPa) 53.3 40.0 water 26.7 13.3 10 20 30 40 50 60 70 80 90 100 Temperature (oC)
Boiling Point and Pressure
Heating / Cooling Curve of Water 140 steam 120 water and steam 100 liquid water 80 Temperature (oC) 60 Heating Cooling 40 ice and water 20 ice -20 Heat added at a constant rate
Gas Collected Over Water
Measuring the Vapor Pressure of a Liquid Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 376
Gas Mixtures and Dalton’s Law
Gases Dissolved in Liquids