CHM1045 Lecture 14 Outline of Last Lecture I Oxidation number II Types of Oxidation Reduction Reactions III The Activity Series for Halogens IV Chemistry in Action Breath Analyzer V Solution Stoichiometry VI Gravimetric Analysis VII Titrations Outline of Current Lecture I Physical Characteristics of Gases II Apparatus for Studying the Relationship Between Pressure and Volume of a Gas III Variation in Gas Volume with Temperature at Constant Pressure IV Charles s and Gay Lussac s Law V Avogadro s Law VI Ideal Gas Equation VII How Gas Laws Work Current Lecture Chapter 5 Gases Elements that exist as gases at 250 C and 1 atmosphere H N O F Cl He Ne Ar Kr Xe Rn Physical Characteristics of Gases Gases assume the volume and shape of their container Gases are the most compressible state of matter Gases well mix evenly and completely when confined to the same container Gases have much lower densities then liquids and solids Pressure Force Area force mass acceleration Units of Pressure 1 pascal pa 1N M2 1 atm 760 mmHg 760 torr 1 atm 101 325 Pa Example 1 The pressure outside a jet plane flying at high altitude falls considerably below standard atmospheric pressure Therefore the air inside the cabin must be pressurized to protect the passengers What is the pressure in atmospheres in the cabin if the barometer reading is 688 mmHg 688 mm Hg pres Atm 688 mm Hg 1 atm 905 atm 760 mm Hg Example 2 The atmospheric pressure in San Francisco on a certain day was 732 mmHg What was the pressure in kPa 732 mm Hg pres K Pa 732 mm Hg 101 325 Pa 1 K Pa 97 6k Pa 760 mm Hg 1000 Pa Manometers used to measure gas pressure Closed tube measure below atmosphere pressure Open tube measure above atmosphere pressure Apparatus for Studying the Relationship Between Pressure and Volume of a Gas As P h increases V decreases Boyles Law P a 1 V P x V constant P1 x V1 P2 x V2 Constant temperature Constant amount of gas Variation in Gas Volume with Temperature at Constant Pressure As T increases V increases Charles s Gay Lussac s Law VaT V constant x T V1 T1 V2 T2 Charles s and Gay Lussac s Law Charles s law Temperature must be in Kelvin T K t 0C 273 15 V1 T1 V2 T2 At constant pressure Constant amount of gas Gay Lussac s law P1 T1 P2 T2 At constant volume Constant amount of gas Avogadro s Law V a number of moles n V constant x n V1 n1 V2 n2 Constant temperature Constant pressure Ideal Gas Equation Boyle s law P a 1 V at constant n and T Charles s law V a T at constant n and P Avogadro s law V a n at constant P and T V a nt P V constant x nt P R nt P R is the gas constant PV nRT The conditions 0 0C and 1 atm are called standard temperature and pressure STP PV nRT R PV 1 atm 22 414L nT 1 mol 273 15 K R 0 082057 L atm mol K How Gas Laws Work Ideal gas law works when nothing is changing What if we have a pressure change a volume change a temperature change or a change in the number of moles Example 3 Sulfur hexafluoride SF6 is a colorless and odorless gas Due to its lack of chemical reactivity it is used as an insulator in electronic equipment Calculate the pressure in atm exerted by 1 82 moles of the gas in a steel vessel of volume 5 43 L at 69 5 C N 1 82 mol V 5 43L T 342 65 K 69 5 273 15 342 65 K PV nRT p 1 82m 082057 L atm Mol K 342 65K 5 43 L 9 42 atm Example 4 Calculate the volume in L occupied by 7 40 g of NH 3 at STP Volume 7 40 g of NH3 STP T 0 C 273 15K P 1 atm 7 40g NH3 1 mol NH3 435 mol NH3 17 024 g NH3 PV nRT 435 mol 08257 L atm mol k 273 15 1 atm 9 74 L Example 5 An inflated helium balloon with a volume of 0 55 L at sea level 1 0 atm is allowed to rise to a height of 6 5 km where the pressure is about 0 40 atm Assuming that the temperature remains constant what is the final volume of the balloon V1 55 L P1 1 atm V2 P2 40 atm P1V1 P2V2 1 atm 55 L 40 atm V2 V2 1 4L Example 6 Argon is an inert gas used in lightbulbs to retard the vaporization of the tungsten filament A certain lightbulb containing argon at 1 20 atm and 18 C is heated to 85 C at constant volume Calculate its final pressure in atm P1 P2 T1 T2 P1 1 20 atm T1 18 C 291 5 K P2 T2 85 C 358 15 K P2 P1 T2 T1 1 20 358 15k 1 48 atm 291 5 Example 7 A small bubble rises from the bottom of a lake where the temperature and pressure are 8 0 C and 6 4 atm to the water s surface where the temperature is 25 C and the pressure is 1 0 atm Calculate the final volume in mL of the bubble if its initial volume was 2 1 mL T 8 0 C 281 5 K T2 25 C 298 15 K P1 6 4 atm P2 1 0 atm V2 V1 2 1 mL P1V1 P2V2 T1 T2 V2 6 4 atm 2 1ml 298 15 281 5 1 0 atm V2 14 2mL 4007 136 281 5
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