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Dispatch Draw a picture of a gas in a container. Then answer the following questions: 1. What sort of path do the molecules travel in? 2. Do they all move at the same speed? 3. When temperature increases, what happens to the motion of the particles? 4. What happens when they collide with the walls of the container? 5. Why is it possible to compress a gas? 6. How does a gas exert pressure? 1 Kinetic Theory of Gases Boyle’s Law, Charles’s Law Gay-Lussac’s Law, Avogadro’s Law 2 Pressure of a Gas Depends on: • Number of molecules • Volume in which they are contained • Average kinetic energy of molecules 3 Boyle’s Law If the amount and temperature of a gas remain constant, the pressure exerted by the gas varies inversely with the volume. P 1/V or PV = k 4 Applying Boyle’s Law P1V1 = P2V2 If some oxygen gas collected at 760 mm Hg is allowed to expand from 5.0 L to 10.0 L without changing the temperature, what pressure will the oxygen gas exert? 380 mm Hg 5 Charles’s Law The volume of a quantity of gas, held at a constant pressure, varies directly with the Kelvin temperature. VT or V = kT 6 Applying Charles’ Law V1/T1 = V2/T2 A 225 mL volume of gas is collected at 58.0 oC. What volume would this sample of gas occupy at standard temperature, assuming pressure remains constant. 186 mL 7 Combining Boyle’s and Charles’ Laws P1V1 = P2V2 T1 417 mL T2 The volume of a gas measured at 755 mm Hg and o 23.0 C is 455 mL. What is the volume of the gas at STP? 8 Sample Problem At STP, the volume of a gas is 325 mL. What volume does it occupy at 20.0 oC and 756 mm Hg? 351 mL 9 Sample Problem A gas occupies a volume of 245 mL at 30.0 oC and 746 mm Hg. Assuming no change in pressure, at what temperature will the gas occupy a volume of 490. mL? 606 K 10 Sample problem A chemist collects 8.00 mL of gas at STP. If the temperature remains constant, at what pressure will the gas volume be reduced to 4.00 mL? 1520 mm Hg 11 Gay-Lussac’s Law The pressure of a quantity of gas, held at a constant volume, varies directly with the Kelvin temperature. PT or P = kT 12 Avogadro’s Law The volume of a quantity of gas, held at a constant temperature and pressure, varies directly with the number of moles. Vn or V = kn 13