Chapter 7 complete - Lecture 20: Gases Goals: Describe the...

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Lecture 20: Gases Goals: Describe the kinetic molecular theory of gases and the properties of gases. Learn the units of measurement used for pressure and how to convert from one unit to another. Use Boyle’s law to determine the pressure or volume of a certain amount of gas at a constant pressure. Outline (Timberlake 7.1-7.4): Properties of Gases (7.1) Gas Pressure (7.2) Pressure and Volume (7.3) Temperature and Volume (7.4) Problems for Extra Practice: 7.1, 7.3, 7.5, 7.7, 7.9, 7.11, 7.13, 7.15, 7.17, 7.19, 7.23, 7.25, 7.27
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Helium He 4.0 Neon Ne 20.2 Argon Ar 39.9 Hydrogen H 2 2.0 Nitrogen N 2 28.0 Nitrogen Monoxide NO 30.0 Oxygen O 2 32.0 Hydrogen Chloride HCl 36.5 Ozone O 3 48.0 Ammonia NH 3 17.0 Methane CH 4 16.0 Substances that are Gases under Normal Conditions Substance Formula MM (g/mol)
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Kinetic Theory of Gases A gas consists of small particles that • move rapidly in straight lines • have essentially no attractive (or repulsive) forces • are very far apart • have very small volumes compared to the volumes of the containers they occupy • have kinetic energies that increase with an increase in temperature
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Properties of Gases • Gases are described in terms of four properties: pressure ( P ), volume ( V ), temperature ( T ), and amount ( n ).
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Gas pressure • is the force acting on a specific area Pressure ( P ) = force area • has units of atm, mmHg, torr, lb/in. 2 and kilopascals(kPa). 1 atm = 760 mmHg (exact) 1 atm = 760 torr (exact) 1 atm = 14.7 lb/in. 2 1 atm = 101.325 kPa Gas Pressure
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A. What is 475 mmHg expressed in atmospheres (atm)? 1) 475 atm 2) 0.625 atm 3) 3.61 x 10 5 atm B. The pressure in a tire is 2.00 atm. What is this pressure in mmHg? 1) 2.00 mmHg 2) 1520 mmHg 3) 22 300 mmHg Learning Check
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Atmospheric Pressure Atmospheric pressure • is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth
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Atmospheric Pressure (continued) Atmospheric pressure • is about 1 atmosphere at sea level • depends on the altitude and the weather • is lower at high altitudes where the density of air is less • is higher on a rainy day than on a sunny day
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Barometer A barometer • measures the pressure exerted by the gases in the atmosphere • indicates atmospheric pressure as the height in mm of the mercury column
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A. The downward pressure of the Hg in a barometer is _____ the pressure of the atmosphere. 1) greater than 2) less than 3) the same as B. A water barometer is 13.6 times taller than a mercury barometer (D Hg = 13.6 g/mL) because 1) H 2 O is less dense 2) H 2 O is heavier 3) air is more dense than H 2 O Learning Check
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Boyle’s Law Boyle’s law states that • the pressure of a gas is inversely related to its volume when T and n are constant • if the pressure ( P ) increases, then the volume ( V ) decreases
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In Boyle’s law • The product P x V is constant as long as T and n do not change. P 1 V 1 = 8.0 atm x 2.0 L = 16 atm L P 2 V 2 = 4.0 atm x 4.0 L = 16 atm L P 3 V 3 = 2.0 atm x 8.0 L = 16 atm L P 1 V 1 = 16 atm L = P 2 V 2 • Boyle’s law can be stated as P 1 V 1 = P 2 V 2 ( T , n constant) PV Constant in Boyle’s Law
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Solving for a Gas Law Factor The equation for Boyle’s law can be rearranged to solve for any factor.
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This note was uploaded on 01/18/2012 for the course CHEM 120A taught by Professor Leahmiller during the Fall '11 term at University of Washington.

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Chapter 7 complete - Lecture 20: Gases Goals: Describe the...

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