CHM1045 Lecture 16Outline of Last LectureI. Density CalculationII. Molar Mass a Gaseous SubstanceIII. Gas StoichiometryIV. Dalton’s Law of Partial PressuresV. Mole fraction (Xi ) = Ni/NrVI. Collecting a Gas over WaterOutline of Current Lecture:I. Kinetic Molecular Theory of GasesII. Kinetic theory of gases and..III. Gas diffusionIV. Gas effusionV. Deviations from Ideal BehaviorCurrent LectureKinetic Molecular Theory of Gases1. A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions. The molecules can be considered to be points; that is, they possess mass but have negligible volume.2. Gas molecules are in constant motion in random directions, and they frequently collide with one another. Collisions among molecules are perfectly elastic.3. Gas molecules exert neither attractive nor repulsive forces on one another.4. The average kinetic energy of the molecules is proportional to the temperature of the gas in kelvins. Any two gases at the same temperature will have the same average kinetic energyKE = ½ mu2Kinetic theory of gases and..• Compressibility of Gases• Boyle’s LawP a collision rate with wall Collision rate a number densityNumber density a 1/VP a 1/V• Gay-Lussac’s LawP a collision rate with wallCollision rate a average kinetic energy of gas moleculesAverage kinetic energy a TP a T• Avogadro’s LawP a collision rate with wallCollision rate a number densityNumber density a nP a n• Dalton’s Law of Partial PressuresMolecules do not attract or repel one anotherP exerted by one type of molecule is unaffected by the presence of another gasPtotal = SPi- The distribution of speeds for nitrogen gas molecules at three different temperatures- The distribution of speeds of three different gases at the same temperatureGas diffusion is the gradual mixing of molecules of one gas with molecules of another byvirtue of their kinetic properties.Gas effusion is the process by which gas under pressure escapes from one compartmentof a container to another by passing through a small opening.urms = 3RTMr1r2M2Example 1: A flammable gas made up only of carbon and hydrogen is found to effuse through a porous barrier in 1.50 min. Under the same conditions of temperature and pressure, it takes an equal volume of bromine vapor 4.73 min to effuse through the same barrier. Calculate the molar mass of the unknown gas, and suggest what this gas might be.1.50 min = √ M/159.8 g/mol4.73 min M= (1.50 min) 2 * 159.8 g/mol (4.73 min) = 16.1g./molDeviations from Ideal Behavior1 mole of ideal gasPV = nRTN= PV = 1.0
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