Gas Laws Properties of Gases Gas Pressure

Some workers cleaned the outside of this tanker car with very hot water one afternoon. When they came back in the morning, it looked like this! What do you think happened to this tanker car?

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

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

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

The Nature of Gases Gases are compressible Gases have low densities 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 Density of a solid or liquid = g/mL Density of a gas = g/L

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

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

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

Barometers

Learning Check 1) greater than 2) less than 3) the same as If a barometer reads 760 mm Hg, the downward pressure of the Hg in a barometer will be_____ the weight of 1 atmosphere. 1) greater than 2) less than 3) the same as

Solution If a barometer reads 760 mm Hg, the downward pressure of the Hg in a barometer will be the same as the weight of 1 atmosphere.

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

Learning Check 1) The weight of the atmosphere pushes it 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 than the straw 3) There is empty space in the straw 4) The pressure in your mouth is lower than the atm Could you drink a soda this way on the moon? 1) yes 2) no 3) maybe Why or why not?

Solution 1) The weight of the atmosphere pushes it 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 4) The pressure in your mouth is lower than the atm Could you drink a soda this way on the moon? 2) no Why or why not? Low atmospheric pressure

Types of Pressure Units Pressure Used in 760 mm Hg or 760 torr Chemistry 14.7 lb/in.2 (psi) U.S. pressure gauges 101,325 Pa (Pascal) SI Unit - Weather in all countries except U.S. 1.013 bars Physics and astronomy

Learning Check 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) 1.52 x 103 mmHg 3) 2.23 x 104 mm Hg 760 mm Hg = 1 atm 760 mm Hg = 14.7 psi

Solution A. What is 475 mm Hg expressed in atm? 475 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 760 mmHg = 1.52 x 103 mmHg 14.7 psi (B)