CHM1045 Lecture 15 Outline of Last 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 Outline of Current Lecture I Density Calculation II Molar Mass a Gaseous Substance III Gas Stoichiometry IV Dalton s Law of Partial Pressures V Mole fraction Xi Ni Nr VI Collecting a Gas over Water Current Lecture Density d Calculations D m PM V RT Molar Mass M of a Gaseous Substance M dRT P m is the mass of gas in g M is the molar mass of the gas d is the density of the gas in g L Example 1 Calculate the density of carbon dioxide CO2 in grams per liter g L at 0 990 atm and 55 C D PM 900atm 44 01g mol 1 62g L RT 0 0821 L atm K mol 328K V nRT 1mol 0821 L atm K mol 328K 27 2 L P 990 atm D 44 01g 27 2L 1 62 g L Example 2 A chemist has synthesized a greenish yellow gaseous compound of chlorine and oxygen and finds that its density is 7 71 g L at 36 C and 2 88 atm Calculate the molar mass of the compound and determine its molecular formula M dRT N PV RT 7 71g L 0821 L atm K mol 36 273 K 2 88atm 67 9 g mol 2 88 atm 1 00L 0 0821 L atm K mol 309K M mass of moles 7 71g 1135 mol 67 9 g mol Gas Stoichiometry Example 3 Calculate the volume of O2 in liters required for the complete combustion of 7 64 L of acetylene C2H2 measured at the same temperature and pressure Volume of O2 7 64 L C2H2 5 L O2 2L C2H2 19 1 L Dalton s Law of Partial Pressures V and T are constant Ptotal P1 P2 Consider a case in which two gases A and B are in a container of volume V Pa NaRT Na is the number of moles of A V PB NBRT V PT PA PB Pa Xa PT nB is the number of moles of B Xa Na Na NB XB NB Na NB PB X B PT P X P i i T mole fraction Xi Ni Nr Collecting a Gas over Water 2KClO3 s PT PO cPH O 2KCl s 3O2 g
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