# Chap 12 - 12 Gases and Kinetic Molecular Theory 1...

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1 12 Gases and Kinetic Molecular Theory

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2 Comparison of Solids, Liquids, and Gases The density of gases is much less than that of solids or liquids. Densities (g/mL) Solid Liquid Gas H 2 O 0.917 0.998 0.000588 CCl 4 1.70 1.59 0.00503 Gas molecules are very far apart compared to liquids and solids.
3 Composition of the Atmosphere and Some Common Properties of Gases Gas % by Volume N 2 78.09 O 2 20.94 Ar 0.93 CO 2 0.03 He, Ne, Kr, Xe 0.002 CH 4 0.00015 H 2 0.00005 Composition of Dry Air

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4 Composition of the Atmosphere and Some Common Properties of Gases Gases can be compressed. Gases exert pressure on their surroundings. Gases expand without limit. Gases diffuse into each other (miscible) Gases are described in terms of their volume (V), temperature (T), pressure (P), and moles of gas (n)
5 Pressure Pressure is force per unit area. lb/in 2 N/m 2 1 atm = 760 mmHg = 760 torr

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6 Pressure Atmospheric pressure is measured using a barometer. Hg density = 13.6 g/mL
7 Pressure Definitions of standard pressure 76 cm Hg 760 mm Hg 760 torr 1 atmosphere 101.3 kPa

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8 Boyle’s Law: The Volume-Pressure Relationship Boyle’s Law states that the volume of a gas is inversely proportional to its pressure if the moles of gas and the temperature of the gas remain constant. V 1/P V= k (1/P) or PV = k if n and T remain constant
9 Boyle’s Law: The Volume-Pressure Relationship P 1 V 1 = k for one sample of a gas P 2 V 2 = k for a second sample of a gas n and T of the two gases are the same Boyle’s Law can be written as P 1 V 1 = P 2 V 2

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10 Boyle’s Law: The Volume-Pressure Relationship Example 12-1: At 25 o C a sample of He has a volume of 4.00 × 10 2 mL under a pressure of 7.60 × 10 2 torr. What volume would it occupy under a pressure of 2.00 atm at the same T? V 1 = 4.00 × 10 2 mL V 2 = ? P 1 = 7.60 × 10 2 torr P 2 = 2.00 atm 1520 torr
11 Boyle’s Law: The Volume-Pressure Relationship 2 1 1 2 2 2 1 1 P V P V V P V P = =

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12 Boyle’s Law: The Volume-Pressure Relationship () ( ) torr 1520 mL . 400 torr 760. V P V P V V P V P 2 2 1 1 2 2 2 1 1 = = =
13 Boyle’s Law: The Volume-Pressure Relationship ( )( ) mL 10 00 . 2 V torr 1520 mL . 400 torr 760. V 2 2 2 × = =

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