Chapter_10-Gases

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

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Chapter 10. Gases Gases

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Chapter 10. Gases Characteristics of gases Highly compressible; Infinitely expandable; Negligible interactions between molecules;
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 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.
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 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
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 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.
Chapter 10. Gases Modern compact manometers Front view Back view Pressure- sensing thin wall copper tube

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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
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 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.
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. Equal volumes of gases at the same P and T contain equal number of molecules.

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