Characteristics of Gases

Ex 1 GASES Characteristics of Gases Some nitrogen gas is in a 2.00-L tank at a pressure of 3.00 atm. The tank is connected to a 5.00-L tank that is completely empty (evacuated), and a valve connects the two tanks., If the valve is opened, determine the total pressure in this two-tank system after the nitrogen stops flowing. No temperature change occurs in the process. Charles’s Law Pressure Barometers and Atmospheric Pressure Avogadro’s Law Gas Laws Ex 2 A certain mass of C3H6 reacts completely with an excess of ammonia and oxygen to give 38.2 L of C3H3N at 75°C and P = 1.00 atm. If the same mass of C3H6 reacts Boyle’s Law completely at 350°C and P = 1 atm, what volume of C3H3N can be collected at the higher temperature? 2 C3H6(g) + 2 NH3(g) 1 The Ideal-Gas Equation + 3 O2(g) ! 2 C3H3 N(g) + 6 H2O(g) 2 Applications of the Ideal-Gas Equation Gas Density and Molar Mass Ex 3 Ex 4 A gas is in a container with a movable piston under a pressure of 6.4 atm. The volume of the container is increased by a factor of 4.5 by moving the piston. The absolute temperature is simultaneously doubled. Calculate the pressure of the gas after these changes. Ex 5 Calculate the density of gaseous SF6 at a temperature of 27°C and a pressure of 0.873 atm. At what temperature (in K) does 29.8 g of O2 gas have a pressure of 2.00 atm in a 10.0-liter tank? 3 4 Gas Mixtures and Partial Pressures Ex 6 The empirical formula of a gaseous fluorocarbon is CF2. If 1.55 g of this compound occupies 0.174 L at STP determine the molecular formula of this compound. Partial Pressure Mole Fraction Ex 7 An important process for the production of acrylonitrile (C3H3N) is given by the reaction: 2 C3H6(g) + 3 O2(g) ! 2 C3H3 N(g) + 6 H2O(g) + 2 NH3(g) A 150.0-L reactor is charged to the following partial pressures at 25°C: PC3H6 = 4.93 atm, PNH3 = 7.90 atm, PO2 = 14.8 atm What mass of acrylonitrile can be produced from this mixture? Ex 9 The partial pressure of O2(g) in a mixture of O2 (g) and H2(g) is 2.54 atm. The total pressure of the mixture is 3.92 atm. Determine the partial pressure of H2 (g), and the mole fraction of each gas in the mixture. Ex 8 A 0.326-g sample of XH2 reacts with water according to the equation XH2(s) + 2 H2O(l) ! X(OH)2(s) + 2 H2(g) 3 Ex 10 A gas mixture at room temperature contains 4.3 mol of H2 and 8.2 mol of N2 . (a) Compute the mole fraction of N2 in the mixture. The hydrogen evolved is found to have a volume when dry of 375 cm at 21°C and 1.00 atm. What is the atomic mass of X? (b) The mixture is then heated, and the N2 starts to react with the H2 to give NH3: N2(g) + 3 H2 (g) ! 2 NH3(g) The reaction is stopped when 2.8 mol of NH3 is present. Determine the mole fraction of N2 in this new mixture. 5 6 Collecting Gases over Water Molecular Motion The Kinetic Theory of Gases Temperature and Molecular Motion Ex 11 Acetylene (C2 H2) can be made by allowing calcium carbide to react with water. CaC2(s) + 2 H2O(l) ! C2H2(g) + Ca(OH)2(aq) You place 2.65 g of CaC2 in excess water and collect the acetylene over water. (a) Calculate the theoretical yield of acetylene (in grams). (b) After reaction, the volume of the acetylene and water vapor is 795 mL at 25.0°C and a pressure of 0.967 atm. Calculate the percent yield of acetylene. The vapor pressure of water at 25.0°C is 0.0313 atm. 7 Distribution and Molecular Speeds 8 Mean Free Path and Diffusion Real Gases Real gases obey the ideal gas law at low pressures only. Van der Waals Equation of State Gaseous Effusion Ex 12 Methane (CH4 ) effuses through a small opening at the rate of 1.30 " 10 -8 mol/s. An -9 unknown gas effuses through the same opening at the rate of 5.42 " 10 mol/s (at the same T & P as the methane). Determine the molar mass of the unknown gas. Ex 13 9 Oxygen is supplied to hospitals and chemical laboratories under pressure in large steel cylinders. Typically, such a cylinder has an internal volume of 28.0 L and contains 6.80 kg of oxygen. Use the van der Waals equation to estimate the pressure inside such a cylinder at 20°C. 10