Atmospheric Pressure Measurement Accomplished with barometer Units of standard pressure o 760 mm Hg 760 torr 29 92 in Hg o 1 atmosphere o 101 3 kPa kilopascal o 14 696 psi lb in2 o 10 33 m H2O 33 90 ft H2O Gas Laws Volume Pressure Relationships Boyle s law compressibility of gases V is inversely proportional to 1 P or V constant x 1 P or PV constant PV mRT P2V1 P2V2 constant for a sample of gas Pressure volume inversely proportional at constant T ConcepTest A gas sample has a volume of 1 L at 1 atm Which statement is true about the volume of the same gas sample at the same temperature if the pressure is lower to 0 5 atm A 0 5 L B 0 5L C 1 0 L D 2 0 L E 2 0 L F can t be determined from the information given ConcepTest A sample of He has a volume of 0 40 L at 700 torr 0 921 atm What volume would the He occupy at 1 1 atm 0 335 L A 0 335 mL B 33 5 L C 335 mL D 0 478 mL E 478 mL F none of these Charles s Law Volume Temperature Relationships V directly proportional to T T in K or V constant x T or V T constant ConcepTest A gas sample has a volume of 1 L at 0C Which statement is true about the volume of the same gas sample at the same pressure if the temperature is raised to 546 K A 0 5 L B 0 5 L C 1 0 D 2 0 L E 2 0 L F can t be determined from the information given ConcepTest A filled automobile airbag contains 70 L of nitrogen at 43 C 109 F 316 K in Athens If the temperature at Vostok station Antarctica reached 89 C 128 F 184 K what would happen to the airbag volume there Assume the pressure is the same A 70 L bag might burst D 4 L Ooooh B 70 L No problem E none of these C 41 L This might hurt Standard Temperature and Pressure Definition STP or Standard temperature and pressure Reference point for some gas calculations Standard P 1 atm or 101 3 kPa Standard T 273 K P1V1 T1 P2V2 T2 ConcepTest A sample of nitrogen gas N2 occupies 550 mL at 55 0 C under a pressure of 550 torr What volume would it occupy at STP 0 724 atm 328 K 273 A 331 mL B 458 mL C 1976 mL D none of these Combined Gas Law Boyle s Law pressure volume PV constant Charles s Law volume temp V T constant ConcepTest Three identical balloons are each filled to 22 4 L of helium oxygen and methane CH4 at STP Place the filled balloons in order of increasing mass lightest first A helium oxygen methane B helium methane oxygen C oxygen methane helium D methane helium oxygen E oxygen and methane are equivalent Avogadro s Law Standard Molar Avogadro s Law Equal volumes of two gases contain same number of molecules or moles of gas at same T and P At STP one mole of gas has standard molar volume 22 4 L For gases volume is proportional to number of moles Ideal Gas Law summary Boyles law Combination Three laws into one statement V is proportional to nT P Convert into equality V nRT P R is proportionally constant universal gas constant PV nRT 0 0821 L atm mol K ConcepTest Calculate the mass of propane C3H8 in an 8 00 L sample of propane measured at standard conditions A 0 357 g B 15 7 g 1atm 8 00 L x 0 0821 273 K Density of Gases Mass moles x molecular weight M n x MW Density mass per unit volume D m v D n x MW v or n v d MW C 22 4 g D not enough information 0 3569 mol 44 094g mol 15 7 g