Ch 5_020512 - Chapter 5 Gases 5.1 5.2 5.3 5.4 5.5 5.6 5.7...

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2/5/2012 1 Chapter 5: Gases 5.1 Definitions 5.2 The First Laws 5.3 The Ideal Gas Law 5.4 Stoichiometry and Gases 5.5 Mixtures of Gases (Partial Pressures) 5.6 Kinetic Molecular Theory 5.7 Effusion and Diffusion 5.8 Collisions with Container Walls 5.10-11 Real Gases (limited coverage) 1 Definitions: Phases of Matter
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2/5/2012 2 Important Characteristics of Gases 1) Gases are highly compressible An external force compresses the gas sample and decreases its volume; removing the external force allows the gas volume to increase. 2) Gases are thermally expandable When a gas sample is heated, its volume increases; when it is cooled its volume decreases. 3) Gases have low viscosity Gases flow much easier than liquids or solids. 4) Most gases have low densities Gas densities are on the order of grams per liter ,whereas liquids and solids are grams per cm 3 (mL), 1000 times greater. 5) Gases are infinitely miscible Gases mix in any proportion (air is a mixture of many gases). Steam clean the inside of a train tank car, and then seal the top and allow the contents to thermally equilibrate with the surroundings. What will happen?? http://www.youtube.com/watch?v=Zz95_VvTxZM
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2/5/2012 3 Pressure Pressure is force per unit area: SI units: pressure is expressed in newtons per square meter, N/m 2 , the pascal (Pa). 1 Pa = 1 N/m 2 How do we measure the force of a gas ? F P A Barometer Open to atmosphere Closed Vacuum 1 atm 1 atm 1 atm 1 atm The mercury column exerts a force over the cross- sectional area of the tube. The pressure exerted by the mercury column is exactly balanced by the pressure of the atmosphere. The gases in the atmosphere at sea level on a fair day (no storms) exert “one atmosphere” of pressure. P h g d    pressure height accel. due to gravity density
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2/5/2012 4 Measuring the height of the Hg column will tell you what the atmospheric pressure is. Mercury Barometer Units : “ mm Hg (milimeters of mercury) Also known as “ torr ” after Evangelista Torricelli, inventer of the barometer. 1 atm of pressure = 760 mm Hg at sea level on a nice day (no storms) In Breckenridge, CO (elev. 9600 ft) atmospheric pressure is only 520 mm Hg. h h Manometers Manometers operate on the same principle as barometers, but they measure the pressure of an isolated gas sample rather than the whole atmosphere. P gas + h = P atm Note : P atm is obtained from a barometer. P gas = P atm + h
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2/5/2012 5 Common Units of Pressure Unit Atmospheric Pressure Scientific Field Used Pascal (Pa) = N/m 2 ; 1.01325 x 10 5 Pa SI unit; physics, kilopascal (kPa) 101.325 kPa Chemistry bar 1.01325 bar Meteorology, Chemistry atmosphere (atm) 1 atm Chemistry millimeters of mercury 760 mmHg Chemistry, medicine, (mmHg), also called 760 torr biology “torr” pounds per square inch 14.7 lb/in 2 Engineering (psi or lb/in 2 ) The First Gas Laws Gases are relatively easy to measure and observe in a laboratory.
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Ch 5_020512 - Chapter 5 Gases 5.1 5.2 5.3 5.4 5.5 5.6 5.7...

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