Ch5(7-9)Oct6Fa08a

Ch5(7-9)Oct6Fa08a - CHEM 109 General Chemistry University...

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Unformatted text preview: CHEM 109 General Chemistry University of Nebraska Fall 2008 Monday 6 October 2008 ANNOUNCEMENTS: Don't forget UTAC Tues (6 pm) and Thurs (4 pm) in Avery 119 Acetylene (C2H2), an important fuel in welding, is produced in the laboratory when calcium carbide (CaC2) reacts with water: CaC2(s) + 2H2O(l) C2H2(g) + Ca(OH)2(aq) For a sample of acetylene that is collected over water, the total gas pressure (adjusted to barometric pressure) is 738 torr and the volume is 523 mL. At the temperature of the gas (230C), the vapor pressure of water is 21 torr. How many grams of acetylene are collected? Gas Stoichiometry What volume of hydrogen gas will react with 35.5 g of copper (II) oxide to form copper metal and water vapor at 765 torr and 225 0C? The alkali metals [Group 1A(1)] react with the halogens [Group 7A(17)] to form ionic metal halides. What mass of potassium chloride forms when 5.25 L of chlorine gas at 0.950 atm and 293 K reacts with 17.0 g of potassium? Postulates of the Kinetic-Molecular Theory Postulate 1: Particle Volume Because the volume of an individual gas particle is so small compared to the volume of its container, the gas particles are considered to have __________________. Postulate 2: Particle Motion Gas particles are in ___________________________ ______ except when they collide with each other or with the container walls. Postulate 3: Particle Collisions Collisions are ______ therefore the total kinetic energy (Ek) of the particles is constant. (they exchange energy but do not lose any due to friction) Gas Behavior at the Molecular Level Molecular Beam Apparatus Kinetic Energy and Molecular Speed of Gases average kinetic energy of the gas molecules depends on the _______________________________ gases in the same container have the same temperature, thus the same average ____________ if gases have different masses, the only way for them to have the same kinetic energy is to have different average __________ [KE = (mv2)] lighter particles will have a ______________________ than more massive particles at a given temperature, all gases have the same molecular kinetic energy distribution Relationship Between Molar Mass and Molecular Speed Molecular Speed The figures below represent mixtures of neon atom and hydrogen molecules. One of the gas mixtures was used in a pulsed molecular beam experiment. The result of the experiment is shown below. Which of the two gas samples, A or B, was used for this experiment? 8 H2:4 Ne 4 H2:8 Ne Temperature vs. Molecular Speed as the absolute temperature increases, the average velocity of gas particles _________ the distribution function "______________" resulting in more molecules with faster speeds Rates of gas movement __________ movement of gas through a tiny opening into a vacuum __________ mixing of two gases due to their molecular motion Graham's Law of Effusion Graham's Law of Effusion: The rate of effusion of a gas is inversely related to the square root of its _____________. rate of effusion oe 1 M A gas with a smaller molar mass will _____ ________ because the most probable speed of its molecules is higher. RateA RateB = MB MA The Kinetic Molecular Theory rate of diffusion oe 1 M MHCl MNH3 RateNH3 RateHCL = Which molecule will move fastest? Calculate the molar mass of a gas that effuses at a rate 1.462 times N2 rategas A rategas B = Molar Mass gas B Molar Mass gas A rate unknown gas rate N 2 = 1.462 An unknown diatomic gas effuses at a rate that is only 0.355 times that of O2 at the same temperature. What is the identity of the unknown gas? Ratea Rateb = Mb Ma Ideal vs. Real Gases Real gases often do not behave like ideal gases at high pressure or low temperature Ideal gas laws assume 1) no ______________ between gas molecules 2) gas molecules do not ______________________ based on the kinetic-molecular theory at low temperatures and high pressures these assumptions are not valid The Effect of Molecular Volume At high pressure - the amount of space occupied by the molecules is a significant amount of the total volume Real Gas Behavior because real molecules take up space, the molar volume of a real gas is ______ than predicted by the ideal gas law at _________________ The Effect of Intermolecular Attractions At low temperature - the attractions between the molecules is significant Real Gas Behavior because real molecules attract each other, the molar volume of a real gas is ________ than predicted by the ideal gas law at _________________ ...
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Ch5(7-9)Oct6Fa08a - CHEM 109 General Chemistry University...

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