Properties and Importance of Gases

Chapter 7Gases Properties of Gases Gas Pressure LecturePLUS Timberlake

Gases What gases are important for each of the following: O2, CO2 and/or He? A. B. C. D. LecturePLUS Timberlake

Gases What gases are important for each of the following: O2, CO2 and/or He? A. CO2 B. O2/CO2 C. O2 D. He LecturePLUS Timberlake

Some Gases in Our Lives Air: oxygen O2 nitrogen N2 ozone O3 argon Ar carbon dioxide CO2 water H2O Noble gases: helium He neon Ne krypton Kr xenon Xe Other gases: fluorine F2 chlorine Cl2 ammonia NH3 methane CH4 carbon monoxide CO nitrogen dioxide NO2 sulfur dioxide SO2 LecturePLUS Timberlake

The Nature of Gases • Gases are compressible Why can you put more air in a tire, but can’t add more water to a glass full of water? • Gases have low densities Dsolid or liquid = 2 g/mL Dgas 2 g/L LecturePLUS Timberlake

Nature of Gases 1. Why does a round balloon become spherical when filled with air? 2. Suppose we filled this room halfway with water. Where would pressure be exerted? LecturePLUS Timberlake

Nature of Gases • Gases fill a container completely and uniformly • Gases exert a uniform pressure on all inner surfaces of their containers LecturePLUS Timberlake

Kinetic Theory of Gases The particles in gases • Are very far apart • Move very fast in straight lines until they collide • Have no attraction (or repulsion) • Move faster at higher temperatures LecturePLUS Timberlake

Barometers 760 mmHg atm pressure LecturePLUS Timberlake

Learning Check G1 A.The downward pressure of the Hg in a barometer is _____ than (as) the weight of the atmosphere. 1) greater 2) less 3) the same B.A water barometer has to be 13.6 times taller than Hg barometer (DHg = 13.6 g/mL) because 1) H2O is less dense 2) Hg is heavier 3) air is more dense than H2O LecturePLUS Timberlake

Solution G1 A.The downward pressure of the Hg in a barometer is 3) the same (as) the weight of the atmosphere. B.A water barometer has to be 13.6 times taller than Hg barometer (DHg = 13.6 g/mL) because 1) H2O is less dense LecturePLUS Timberlake

Unit of Pressure One atmosphere (1 atm) • Is the average pressure of the atmosphere at sea level • Is the standard of pressure • P = Force Area 1.00 atm = 760 mm Hg = 760 torr LecturePLUS Timberlake

Learning Check G2 When you drink through a straw you reduce the pressure in the straw. Why does the liquid go up the straw? 1) the weight of the atmosphere pushes it 2) the liquid is at a lower level 3) there is empty space in the straw Could you drink a soda this way on the moon? 1) yes 2) no 3) maybe Why or why not? LecturePLUS Timberlake

Solution G2 When you drink through a straw you reduce the pressure in the straw. Why does the liquid go up the straw? 1) the weight of the atmosphere pushes it 3) there is empty space in the straw Could you drink a soda this way on the moon? 2) no Why or why not? Low atmospheric pressure LecturePLUS Timberlake

Types of Pressure Units Pressure Used in 760 mm Hg or 760 torr Chemistry 14.7 lb/in.2 U.S. pressure gauges 29.9 in. Hg U.S. weather reports 101.3 kPa (kilopascals) Weather in all countries except U.S. 1.013 bars Physics and astronomy LecturePLUS Timberlake

Learning Check G3 A. What is 475 mm Hg expressed in atm? 1) 475 atm 2) 0.625 atm 3) 3.61 x 105 atm B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? 1) 2.00 mm Hg 2) 1520 mm Hg 3) 22,300 mm Hg LecturePLUS Timberlake

Solution G3 A. What is 475 mm Hg expressed in atm? 485 mm Hg x 1 atm = 0.625 atm (B) 760 mm Hg B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? 29.4 psi x 1.00 atm x 760 mmHg = 1.52 x 103 mmHg 14.7 psi 1.00 atm (B) LecturePLUS Timberlake

Properties and Importance of Gases