Physical Characteristics of Gases Chapter 10

I. Kinetic-Molecular Theory of Matter - the particles of matter are always moving A. Ideal Gas – an imaginary gas that fits all the following assumptions Gas particles are far apart Collisions of gas particles are elastic (no kinetic energy lost) Gas particles move rapidly No attraction between particles Energy of particles increases at higher temperatures

I. Kinetic-Molecular Theory of Matter B. At the same temperature, all gas particles have the same amount of energy; this means that lighter particles are moving faster than heavier particles K.E. = mv2 K.E. = kinetic energy 2 v = velocity m = mass

I. Kinetic-Molecular Theory of Matter Physical Properties of Gases Expansion - gas particles spread out to fill any container Fluidity Gas particles can slide past one another Gases and liquids are “fluids” Low density Compressibility Diffusion

I. Kinetic-Molecular Theory of Matter D. Real Gases 1. close to ideal gas at normal conditions 2. have volume and attraction between particles 3. deviation from ideal gas is greater when: a. particles are close together (low temperature and high pressure) b. gas is a compound rather than an element

Pressure – force per unit area II. Pressure Pressure – force per unit area P = force (N) Newton area Gas pressure is a result of collisions of gas particles. The pressure depends on the number of gas particles, the temperature and the volume. Instruments used to measure pressure Barometer is used to measure atmospheric pressure Manometer is used to measure the pressure of a gas in a container

II. Pressure D. Units of Pressure 1. mm Hg or torr (1mm Hg = 1 torr) 2. atmospheres (atm) 3. Pascal (Pa) a. the SI unit of pressure (newton (N) is SI unit of force b. atmospheres (atm) c. 1kPa = 1000Pa

II. Pressure E. Standard Pressure 760 mm Hg = 760 torr = 1atm = 101.3kPa F. Standard Temperature and Pressure (STP) 1 atm and 00 C

II. Pressure G. Convert 745 torr to kilopascals H. Convert 245 kilopascals to atmosphere of pressure

III. Gas Laws Boyles’ Law Reducing the volume by one-half doubles the pressure The volume of a fixed mass of gas varies inversely with the pressure at constant temperature P1V1 = P2V2 When a sample of gas is moved from a 2.50L container to a different container, the pressure changes from 101.3 kPa to 40.5 kPa. Find the volume of the new container (temperature constant)

III. Gas Laws Boyles’ Law Reducing the volume by one-half doubles the pressure The volume of a fixed mass of gas varies inversely with the pressure at constant temperature P1V1 = P2V2

III. Gas Laws A. 4. When a sample of gas is moved from a 2.50L container to a different container, the pressure changes from 101.3 kPa to 40.5 kPa. Find the volume of the new container (temperature constant)

III. Gas Laws 5. A balloon is filled with 30.0L of helium at 1.0 atm. Find the pressure at an altitude where the balloon has expanded to 120 L. (temperature constant)

III. Gas Laws B. Charles’Law 1. If the Kelvin temperature is doubled, the volume will double 2. Kelvin Temperature a. absolute zero (0.0 Kelvin) is the temperature at which molecules stop moving b. K = degree Celsius + 273 c. the volume of a fixed mass of gas at constant pressure varies directly with Kelvin temperature

III. Gas Laws B. Charles’Law 3. V1 = V2 Charles’ Law T1 T2 (T must be Kelvin) 4. A sample of gas occupies 7.4 L at 310 degrees Celsius. Find the volume at which the temperature is 25 degrees Celsius. (constant pressure)

III. Gas Laws B. Charles’Law 5. A baloon has a volume of 5.000L. When heated to 63 degrees Celsius, it has a volume of 5.6L. Find the initial Celsius temperature. (constant pressure)

III. Gas Laws C. Gay-Lussac’s Law 1. doubling the Kelvin temperature doubles the pressure 2. the pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature 3. P1 = P2 T1 T2 4. A gas has a pressure of 50.0 torr at 267 degrees Celsius. Find the pressure at -73 degrees Celsius. (constant volume)

III. Gas Laws D. Combined Gas Law 1. P1V1 = P2V2 T1 T2 2. a gas occupies 750.0 cm3 at 27.0 degrees Celsius and 0.0160 atm. Find the Celsius temperature at 10.9 cm3 and 1.00 atm.

III. Gas Laws E. Dalton’s Law of Partial Pressures – the total pressure of a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture. 1. PT = P1 + P2 + … 2. Gases Collected by Displacement of Water a. Atmospheric pressure equals the pressure of the gas plus the pressure of the water vapor Patm = Pgas + PH2O

III. Gas Laws E. 2. b. Table p.899 for vapor pressure of water c. Find the pressure of oxygen gas collected over water at 25 degrees Celsius if the barometer reading is 752 mm Hg