1. Gases The kinetic-molecular theory of gases: A gas consists of particles, atoms, or molecules that move randomly and rapidly. The size of gas particles is small compared to the space between the particles. Gas particles exert no attractive forces on each other. The kinetic energy of gas particles increases with increasing temperature. Gas particles collide with each other, rebound and travel in new directions. Gas Pressure When gas particles collide with the container, they exert pressure (F/A) on the sides. The pressure exerted by the gas incr. with incr. in temp. Gases in the atmosphere exert a pressure called the atmospheric pressure, which decrease with increase in altitude. Measured by a barometer Millimeters of Mercury ( mm Hg) used in a barometer (1 atm. = 760 mm Hg, at sea level). One millimeter of mercury is also called one torr.

2. 1 atm = 760 mm Hg = 760 torr = 1.013 x 10 5 Pa = 101.3 Kpa NB: STP (Standard Temperature and Pressure) refer a pressure of 1 atm. and temperature of 273 K (0 o C). GAS LAWS Four variables define the behaviour of gases: pressure (P), volume (V), temperature (T) and moles (n). 1. BOYLE’s LAW: relates volume and pressure of a gas. The volume occupied by a fixed amount of gas is inversely proportional to the pressure, at constant temperature. P 1 α 1/V 1 The product of the two quantities is a constant P x V = K P 1 V 1 = K, P 2 V 2 = K At constant temp. P 1 V 1 = P 2 V 2

3. 2.CHARLES’ LAW : (relates volume and temperature of a gas) The volume occupied by a fixed amount of gas is directly proportional to its temperature at constant pressure. V 1 α T 1, V 1 /T 1 = k Similarly V 2 α T 2, V 2 /T 2 = k V 1 /T 1 = V 2 /T 2 (at constant pressure) 3.GAY-LUSSAC’S LAW: (relates temperature and pressure of a gas) The temperature of a fixed amount of gas is directly proportional to the pressure exerted by a gas, at constant volume. P 1 α T 1 P 1 /T 1 = k and (P 2 /T 2= = k) P 1 /T 1 = P 2 /T 2, ( at constant volume) 4.COMBINED GAS LAW. P 1 V 1 /T 1 = P 2 V 2 /T 2

4. 4 Gas Laws Boyle’s Law Example If a 4.0-L container of helium gas has a pressure of 10.0 atm, what pressure does the gas exert if the volume is increased to 6.0 L? Step [1] Identify the known quantities and the desired quantity. P 1 = 10.0 atm V 1 = 4.0 L V 2 = 6.0 L known quantities P 2 = ? desired quantity

5. 5 Gas Laws Boyle’s Law Step [2] Write the equation and rearrange it to isolate the desired quantity on one side. P 1 V 1 = P 2 V 2 Solve for P 2 by dividing both sides by V 2. P1V1P1V1 V2V2 = P 2

6. 6 Gas Laws Boyle’s Law Step [3] Solve the problem. P1V1P1V1 V2V2 P 2 == (10.0 atm)(4.0 L) (6.0 L) Liters cancel. =6.7 atm Answer

7. 7 Avogadro’s Law How Volume and Moles are Related Avogadro’s law: When the pressure and temperature are held constant, the volume of a gas is proportional to the number of moles present. If one quantity increases, the other increases as well. Volume Number of moles = constant V n = k Dividing the volume by the number of moles is a constant, k.

8. 8 Avogadro’s Law If the number of moles of gas in a cylinder is increased, the volume of the cylinder will increase as well. V1V1 n1n1 = V2V2 n2n2 This behavior can be explained by the equation: initial conditions new conditions

9. 9 Avogadro’s Law Often, amounts of gas are compared at a set of standard conditions of temperature and pressure, abbreviated as STP. STP conditions are: 1 atm (760 mm Hg) for pressure At STP, 1 mole of any gas has a volume of 22.4 L. 22.4 L is called the standard molar volume. 273 K (0 o C) for temperature

10. 10 The Ideal Gas Law All four properties of gases (i.e., P, V, n, and T) can be combined into a single equation called the ideal gas law. PV = nRT R is the universal gas constant: For atm: R=0.0821 L atm mol K For mm Hg: R = 62.4 L mm Hg mol K

11. 11 Dalton’s Law and Partial Pressures Dalton’s law: The total pressure (P total ) of a gas mixture is the sum of the partial pressures of its component gases. For a mixture of three gases A, B, and C: P total =P A + P B + P C partial pressures of A, B, and C

12. 12 Dalton’s Law and Partial Pressures Sample Problem 6.9 A sample of exhaled air contains four gases with the following partial pressures: N 2 (563 mm Hg), O 2 (118 mm Hg), CO 2 (30. mm Hg), and H 2 O (50. mm Hg). What is the total pressure of the sample? P total =P N 2 + P O 2 + P CO 2 + P H 2 O P total = 563 + 118 + 30. + 50. P total = 761 mm Hg Answer

13. 13 The Ozone Layer Ozone (O 3 ) is a gas formed in the upper atmosphere by the reaction of oxygen molecules (O 2 ) with oxygen atoms (O). Ozone acts as a shield that protects the earth by absorbing destructive ultraviolet radiation. Chlorofluorocarbons (CFCs), once widely used as refrigerants and aerosol propellants, destroy ozone in the upper atmosphere.

14. 14 Carbon Dioxide and Global Warming CO 2 is a greenhouse gas because it absorbs thermal energy that normally radiates from the earth’s surface. Higher levels of CO 2 may contribute to an increase in the average temperature of the earth’s atmosphere, termed global warming.