Chemistry 211 Week 5 Chapter 5 Note Packet
Chemistry 211 Week 5 Chapter 5 Note Packet CHEM 211-003
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This 7 page Class Notes was uploaded by Lucas Kinsey on Sunday October 16, 2016. The Class Notes belongs to CHEM 211-003 at George Mason University taught by Pritha G. Roy in Summer 2016. Since its upload, it has received 40 views. For similar materials see General Chemistry 1 in Chemistry at George Mason University.
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Date Created: 10/16/16
Lucas Kinsey Chemistry 211 Notes Chapter 5 Gases and Kinetic Molecular Theory Behaviors of Gases: - Gas Volume changes significantly with pressure - Gas volume changes significantly with temperature - Gases flow freely - Gases have relatively low densities - Gases form a solution in any proportion Gas Pressure: the force of the accelerated gas particles have on the containting wall Force - Pressure = Area SI unit for pressure = Pascal (Pa) Conversions: - 1 atm (standard atmospheric pressure) = 1.01325 x 105 Pa - 1 mmHg = 133.322 Pa - 760 torr = 1 atm - 1.01325 bar = 1 atm - 14.7 lb = 1 atm ¿2 Ideal Gas: a gas that exhibits a linear relationship between volume, pressure, temperature, and amount (mol) - No true ideal gas ever exists Boyle’s Law: relationship between volume and pressure - Volume is inversely proportional to pressure - “At constant room temperature, the volume occupied by a fixed amount of gas is inversely proportional to the applied external pressure” - V α1 P - PV = Constant (T and n are constant as well) Charles’s Law: relationship between volume and temperature - Volume is directly proportional to temperature - “At constant pressure, the Volume occupied by a fixed amount of gas is directly proportional to its absolute (Kelvin) temperature” - V α T - V = T(constant) Combined Gas Law: relationship between pressure and temperature - At constant volume, the pressure exerted by a fixed amount of gas is directly proportional to the absolute temperature - V ∝ T PV - T = constant Avogadro’s Law: Relationship between amount and volume - Volume is directly proportional to amount - “At fixed temperature, and pressure, the volume occupied by a gas is directly proportional to the amount (mol) of gas” - V ∝ n(mol) - V = n(mol) (constant) **equal volumes of any ideal gas contain an equal number of moles of particles STP: standard temperature and pressure @ 1 atm Standard Molar Volume: 1 mol of an ideal gas @ STP - Standard Molar Unit = 22.4141 L Ideal gas Law: the combination of all the gas laws PV - = R R is a proportionalaity constant known as the nT universal gas constant atm∗L - PV = nRT R = mol∗K Initial to Final: - P1V 1n 1 1 1 == P 2 2n 2 2 2 P V P V - When R is the same -- 1 1= 2 2 n1T1 n2T2 Solving 2 types of Gas Problems: - There is change in one of the four variables resulting in a change in another, while the other variables remain constant (2 constants, 2 changes, initial vs final) - One Variable is unknown and no change occurs o Step 1) Summarize changing gas variables (constants and variables) o Step 2) Convert Units o Step 3) Rearrange the ideal gas law to obtain the needed relationships of the variables Density of Gas: - Differences in density often depend on differences in molar mass - D = m V m - PV = RT μ P∗μ - D = RT - Density of a gas is directly proportional to its molar mass - Density of a gas is inversely proportional to the temperature Molar Mass of a Gas: - Through rearrangement of the ideal gas law, we can find the molar mass of an unknown gas m PV mRT - n(mol) = = ?μ= μ RT PV The ideal gas low holds true for virtually any gas at ordinary conditions, whether it is a pure gas or a mixture of gases such as air b/c 1. Gases mix homogeneously 2. Each Gas in a mixture behaves as if it were the only gas present Dalton’s Law of Partial Pressures: - When water vapor is added to dry air, the total air pressure increases by the pressure of the water vapor o P humid adryaiaddedwater vapor - Each gas in a mixture exerts partial pressure equal to the pressure it would hold by itself - “In a mixture of unreacted gases, the total pressure is the sum of the partial pressures of the individual gases” o P tota1+P2+P 3 n1RT n2RT (1+n2)T ntotal o P tota1+P2= V + V = V = V Mole Fraction (X): each component in a mixture contributes a fraction of the total number of moles in the mixture - X*100 = Mole % - X = molof gasa totalamount(mol) **Partial Pressure of a gas: PA=X AP total Vapor Pressure: when water is in contact with a gas it partially evaporates on contact and contributes to the gas pressure Vapor Pressure of Water @ Different Temperatures °C P °C P T( ) H2O (torr) T( ) H2O(torr) 0 4.6 40 55.3 5 6.5 45 71.9 10 9.2 50 92.5 12 10.5 55 118.0 14 12.0 60 149.4 16 13.6 65 187.5 18 15.5 70 233.7 20 17.5 75 289.1 22 19.8 80 355.1 24 22.4 85 433.6 26 25.2 90 525.8 28 28.3 95 633.9 30 31.8 100 760.0 35 42.2 Stoichiometric Road Map of Gas Laws: P ,V ,T o Amount Amount P ,V ,T o 1 1 1 (mol) of gas (mol) of gas 2 2 2 f gas A f gas A ^^Idea ^^Molar ^^Idea l Gas Ratio from l Gas Law balanced Law equation Kinetic Molecular Theory: Postulate 1: Particle volume, a gas consists of a large collection of individual particles with empty space between them, each particle is a point of mass Postulate 2: Particle motion, particles have constant linear motion until collision occurs Postulate 3: Particle collisions, elastic, therefore the energy is conserved and exchanged. Total kinetic energy is still constant however RMS Speed ( μRMS¿ : a particle moving at this speed has the average kinetic energy - μRMS= 3RT √ μ Effusion: the process in which a gas escapes through a tiny hole in its container into an evacuated space Graham’s Law of Effusion: the rate of effusion of a gas is inversely proportional to the square root of its molar mass - Rate of effusion ∝ 1 √μ Diffusion: the movement of one gas through another - Graham’s Law of Diffusion is the same as Graham’s law of Effusion - When you have 2 gases of equal pressure: Ratgasa πgasb o Rate = μ gasb√ gasa - Reason: lighter molecules have higher average speeds than heavier molecules, so move farther in a given time Real Gases (exhibit close-to-ideal behavior): - Gas particles are not points of mass with zero volume, but rather have volumes determined by the sizes of their atoms and the length and directions of their bonds - Attractive and repulsive forces do exist among gas particles because atoms contain charged subatomic particles and many substances are polar - Normal conditions is typically depicted by a high temperature with low pressure PV - At lower pressures, RT Values are lower than ideal values PV - At higher pressures, RT values are greater than ideal values because of particle volume Van der Waals (an adjustment to the ideal gas law): an2 - ( ) 2 (−nb )nRT v - a and b are Van der Waals constants (specific for given gases and is usually given in the problem being asked) - a stands for the number of distributed electrons - b stands for the particle volume - At normal conditions, Van der Waals equation becomes the ideal gas equation