Chapter_10-Gases

Chapter_10-Gases - Chapter 10. Gases Chapter Gases Chapter...

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Chapter 10. Gases Chapter 10. Gases Gases
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Chapter 10. Gases Chapter 10. Gases Characteristics of gases Highly compressible; Infinitely expandable; Negligible interactions between molecules;
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Chapter 10. Gases Chapter 10. Gases Gas pressure P = F/A Pressure, Pa Force, N Area, m 2 Gas pressure is an isotropic value: i.e. it acts uniformly in/from all directions. Definition: Pressure is a force applied to a certain area.
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Chapter 10. Gases Chapter 10. Gases Fluidic pressure is an isotropic value: pressure force is applied perpendicularly to a solid surface This is the reason that this perpetuum mobilus will not work.
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Chapter 10. Gases Chapter 10. Gases Atmospheric pressure Barometer – the device to measure atmospheric pressure (E. Torricelli) Principle of action : Atmospheric pressure of air and pressure of liquid mercury column equilibrate each other. Thus we can measure pressure in “mm Hg”.
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Chapter 10. Gases Chapter 10. Gases Atmospheric pressure Atmospheric pressure drops with the height. Typical force that atmosphere of the Earth applies to human body surface is an equivalent of 10 to15 ton (~20,000 to 30,000 lb). Standard atmospheric pressure (average air pressure at sea level): 1 atm = 760 mm Hg = 101,325 Pa
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Chapter 10. Gases Chapter 10. Gases Different units of pressure 1 Pa = 1 N / 1 m 2 (SI unit) 1 atm = 760 mm Hg = 101,325 Pa 1 mm Hg = 1 Torr 1 bar = 100,000 Pa 1 atm = 14.7 lb/in 2 (psi)
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Chapter 10. Gases Chapter 10. Gases Mercury manometer Principle of action : Pressure of a gas in a vessel is equilibrated against atmospheric pressure plus pressure of mercury. P gas > P atm P gas < P atm Marometer – the device to measure gas pressure in vessels.
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Chapter 10. Gases Chapter 10. Gases Modern compact manometers Front view Back view Pressure- sensing thin wall copper tube
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Chapter 10. Gases Chapter 10. Gases Gas laws Four variables are needed to describe the state of a gas (SI units are shown): 1. Temperature, T, K 2. Pressure, P, Pa 3. Volume, V, m 3 4. Amount of gas substance, n, mole
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Chapter 10. Gases Chapter 10. Gases Boyle’s law: PV=const at T=const, n=const V = constant 1/P The volume of fixed amount of gas maintained at constant temperature is inversely proportional to the pressure.
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Chapter 10. Gases Chapter 10. Gases Charle’s law: V/T =const at P=const, n=const: V = constant T Important: in gas formulas the T must be always in K (not in °C or °F). “Absolute zero” The volume of fixed amount of gas maintained at constant pressure is directly proportional to its absolute temperature.
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Chapter 10. Gases Gay-Lussac’s observation (law #1) of combining volumes At given P and T the volumes of reacting gases (and products, if gaseous) are in ratios of small whole numbers.
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Chapter_10-Gases - Chapter 10. Gases Chapter Gases Chapter...

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