Chapter 10 What is pressure Gases Density of an ideal gas Pressure and Boyle s Law Temperature and Charles Law Avogadro s Law Ideal gas equation of state PV nRT d PM RT Molecular Weight of an ideal gas M dRT P Partial Pressures Dalton s Law Kinetic Molecular Theory of gases Ideal Gas Real gases Mary J Bojan Chem 110 1 PRESSURE Pressure force area F newtons A m2 SI Units 1N m2 1Pa Pascal Standard atmospheric pressure 1 atm 1 013x105 Pa 1 atm 760 torr mm Hg 1 atm 14 7 lb in2 real atmospheric pressure varies with altitude and weather What causes atmospheric pressure How big is one atm Mary J Bojan Chem 110 2 Pressure decreases exponentially with altitude WHY Pressure at any altitude depends on weight of gas above it What is pressure Mary J Bojan Chem 110 3 Pressure and altitude Altitude km 0 50 100 200 Mary J Bojan P atm collision frequency sec 1 1 1010 10 3 10 6 10 13 107 103 1 Chem 110 4 Measuring Pressure Barometer used to measure Patm force balance on area Fa A F A These are equal Fa A F A so Fa A Patm Patm gd h where g gravitational constant d density of liquid F A gd h So Patm constant x h Patm height of column of liquid measure P in terms of height of Hg 1 atm 760 torr 760 mmHg Mary J Bojan Chem 110 5 Manometer Used to measure the difference in pressure between open or closed end and that of a gas in a vessel P 0 Mary J Bojan Chem 110 6 What is the pressure of the gas in the bulb 1 Pgas Ph 1 Pgas Ph 2 Pgas Patm 2 Pgas Patm 3 Pgas Ph Patm 3 Pgas Ph Patm 4 Pgas Ph Patm 4 Pgas Ph Patm 5 Pgas Patm Ph 5 Pgas Patm Ph Mary J Bojan Chem 110 7 PVT relationships State of gas described by n P V T n moles P pressure V volume T absolute temperature K Avogadro s Law V of gas at constant T and P is proportional to the number of moles of gas V n P T fixed constant of proportionality is the same for ALL gases Mary J Bojan Chem 110 8 PVT relationships Boyles Law V of a fixed amount of gas at constant T is inversely proportional to P n T fixed V 1 P Mary J Bojan Chem 110 9 PVT relationships Charle s Law V of fixed amount of gas at constant P is proportional to the absolute temperature V T n P fixed So far V 1 P Boyle s law V T Charles s law V n Avogadro s law Mary J Bojan Combining these nT V P Chem 110 10 Ideal Gas Law PV nRT T units K R gas constant Units of R are important L atm R 0 08206 mol K J R 8 314 mol K Example What is the volume V occupied by 1 00 mole of gas at exactly 0 C and 1 atm Mary J Bojan Chem 110 11 Ideal Gas Law STP Standard Temperature and Pressure 0 C and 1 atm VSTP 22 4L mol Note STP for gases is not the same as standard state conditions used for H Mary J Bojan Chem 110 12 Density and Molecular Weight Find the density d of an ideal gas Gather information nM m M molecular weight m mass Units of density g m mass density L V volume Ideal Gas Law n P V RT d density d PM RT nM PM V RT Molecular weight M Mary J Bojan Chem 110 dRT P 13
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