Chapter 10: Gases Part 3: Real GasesChapter 10: Gases Part 3: Real GasesEffusion and DiffusionPractice ProblemCollisions and DiffusionReview of Density and Molar MassPractice ProblemReal Gases Deviate from Ideal BehaviorKMT and Non-Ideal Gas BehaviorReal Gases: At High Pressure, Postulate 2 in KMT is Not TrueReal Gases: At Low Temperature, Postulate 3 in KMT is Not TrueHow Do We Account for This Behavior?Non-Ideal Behavior and Measured PressureNon-Ideal Behavior and Measured Volumevan der Waals EquationPractice ProblemKMT and Non-Ideal Gas Behavior: Does This Make Sense?KMT and Non-Ideal Gas Behavior: Does This Make Sense?KMT and Non-Ideal Gas Behavior: Does This Make Sense?What You Should KnowChapter 10: GasesPart 3: Real GasesCH110 FA11 SAS 1Prepare for Recitation October 20thALEKS Objective 8 due October 18thANGEL Quiz 8, October 20thLecture 22: October 12thLecture 23: October 14thLecture 24: October 17thRead: Ch. 10.1-10.9Additional Preparation: BLB 10: 5,23,30,45,71,75,82-84; Packet 10: 1-15BLB 25: 11,12,25CH110 FA11 SAS 2By the end of Today’s Lecture you should know:Kinetic-molecular theoryReal gases (van der Waals)KEY QUESTIONS: THE BIG PICTUREChapter 10: GasesPart 3: Real GasesWhat does partial pressure mean?What type of mixtures do gasses form?What state equation can we use to describe mixtures of gasses?Remember: macroscopic properties come from microscopic originsHow does the energy of a molecule in a gas compare with intermolecular forces?How can we describe mixtures of gasses?How do real gasses differ from ideal gasses?Effusion and DiffusionCH110 FA11 SAS 3Note: Diffusion is more complicated due to collisions between gas molecules, but it also obeys Graham’s Law.Graham’s Law of Effusion:M2M1r1r2=Effusion: Diffusion:Heavy molecules diffuse (or effuse) more ______ than lighter ones.1Mr proportional toPractice ProblemCH110 FA11 SAS 4An unknown gas effuses at a rate 1.49 times faster than Cl2. What is the molecular weight of the gas?A. 16.0 g/molB. 31.9 g/molC. 47.6 g/molD. 106 g/molE. 157 g/molCollisions and DiffusionCH110 FA11 SAS 5The rate of diffusion follows Graham’s LawAt STP molecules collide ~ 1010times per secondN2speed = 500 m/sbut … … in 1 s it collides 1010timesWhat happens to the MFP as density and pressure decrease?Mean Free Path (MFP):Review of Density and Molar MassCH110 FA11 SAS 6The Ideal Gas LawThe Connection between moles and massThe Ideal Gas Law becomes:The definition of density:Density and the Ideal Gas Law:n moles = m (mass)M (molar mass)d =mVPractice ProblemCH110 FA11 SAS 7Silicon tetrachloride is a starting material for the production of electronics-grade silicon. Calculate the density of pure silicon tetrachloride vapor at 85oC and 758 torr.A. 0.238 g/LB. 5.77 g/LC. 1.00 g/LD. 24.3 g/LE. 0.056 g/LReal Gases Deviate from Ideal BehaviorCH110 FA11 SAS 8For an ideal gas:For a non-ideal gas (a real gas) this is not true for ____ pressure or ___ temperature.Reasons:1. Molecules have finite size.2. Molecules exert attractive forces (IMF)PV = nRTPVnRT= 1PVnRT> 1PVnRT< 1KMT and Non-Ideal Gas BehaviorCH110 FA11 SAS 9Kinetic Molecular Theory has 5 key postulates:1) straight-line motion in random directions2) Molecules are small & have “no” volume3) No intermolecular interactions4) Elastic collisions5) Mean kinetic energy ∝ temperature E = ½ mv2Deviations from ideal gas behavior are caused because gas molecules/atoms have ___________ and have _______________when they are close together.Why does PV = nRT ?Real Gases: At High Pressure, Postulate 2 in KMT is Not TrueCH110 FA11 SAS 10• At low pressures, deviation from ideal behavior is small.• At high pressures, use of the ideal gas law leads to an appearance of larger n.For 1 mole of ideal gas: PV/RT = 1Real Gases: At Low Temperature, Postulate 3 in KMT is Not TrueCH110 FA11 SAS 11• At low T or high P, attractive forces lead to the appearance of a smaller n.(IMF cause molecules to stick together)• As temperature increases the behavior of real gases becomes more ideal.For 1 mole of ideal gas: PV/RT = 1How Do We Account for This Behavior?CH110 FA11 SAS 12High PressureVery High PressureLow PressureAs Temperature increases the behavior of real gases becomes more idealAttractive forces lead to the appearance of a smaller volume or smaller n (depending on which was given)Finite molecular volume leads to repulsion and the appearance of a larger volume or larger nAttractive forces and finite molecular volume have minimal impact@ high temps the kinetic energy overcomes the attractive forcesNon-Ideal Behavior and Measured PressureCH110 FA11 SAS 13• For any gas we can measure P, V, T• But at higher P, the measured P is “too small” because of attractive forcesThe amount of “missing” P is proportional to:1) the size of the attractive forces (a)2) the frequency of collisions (n/V)2To compensate, use:Non-Ideal Behavior and Measured VolumeCH110 FA11 SAS 14• For any gas we can measure P, V, T• But at higher P, the measured V is “too large” because of the finite molecular volume per mole (b)Actual volume:Vactual= Vmeasured– VexcludedTo compensate, use:(BLB Figure 10.25)van der Waals EquationCH110 FA11 SAS 15The Equation of state for REAL gases:The Equation of state for IDEAL gases:PV = nRTnRTnbVaVnP =−+ ))((22Table 10.3 lists van der Waals constants (a,b) for various gas molecules.Practice ProblemCH110 FA11 SAS 16What is the pressure P of 1.0 mol Cl2in a 2.0 L vessel at 273 K?Ideal Gas:van der Waals:a = 6.49L2atmmol2b = 0.0562 L/molKMT and Non-Ideal Gas Behavior:Does This Make Sense?CH110 FA11 SAS 17Kinetic Molecular Theory has 5 key postulates and two have causedproblems:2) Molecules are small & have “no” volume3) No intermolecular interactionsnRTnbVaVnP =−+ ))((22KMT and Non-Ideal Gas Behavior:Does This Make Sense?CH110 FA11 SAS 18Molecules are small & have “no” volume.At LOW Pressure:The volume of the container is ________compared with the volume of the particlesAt HIGH pressures:The volume of the particles becomes ________ and the volume available to the gas is _________ the container volumenRTnbVaVnP =−+ ))((22Gas b (L/mol) SizeNe 0.0171Ar 0.0322Kr 0.0398Xe 0.0510KMT and Non-Ideal Gas Behavior:Does This Make Sense?CH110 FA11 SAS 19Molecules in a gas have no interactions.At LOW Temperature:Intermolecular forces tend to be _________and the KE is insufficient to overcome themAt HIGH Temperature:The KE of the particles becomes ________the
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