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Prentice-Hall © 2008General Chemistry: Chapter 6Slide 1 of 41 Chapter 6: Gases Philip Dutton University of Windsor, Canada Prentice-Hall © 2008 General.

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Presentation on theme: "Prentice-Hall © 2008General Chemistry: Chapter 6Slide 1 of 41 Chapter 6: Gases Philip Dutton University of Windsor, Canada Prentice-Hall © 2008 General."— Presentation transcript:

1 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 1 of 41 Chapter 6: Gases Philip Dutton University of Windsor, Canada Prentice-Hall © 2008 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition

2 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 2 of 41 Contents 6-1Properties of Gases: Gas Pressure 6-2The Simple Gas Laws 6-3Combining the Gas Laws: The Ideal Gas Equation and The General Gas Equation 6-4Applications of the Ideal Gas Equation 6-5Gases in Chemical Reactions 6-6Mixtures of Gases

3 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 3 of 41 Contents 6-7KineticMolecular Theory of Gases 6-8Gas Properties Relating to the KineticMolecular Theory 6-9Non-ideal (real) Gases Focus on The Chemistry of Air-Bag Systems

4 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 4 of Properties of Gases: Gas Pressure Gas Pressure Liquid Pressure P (Pa) = Area (m 2 ) Force (N) P (Pa) = g ·h ·d d(Hg) = g/cm 3 (0°C) g = m/s 2 - acceleration due to gravity h - height of the liquid column d - density of the liquid

5 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 5 of 41 Barometric Pressure Standard Atmospheric Pressure 1.00 atm 760 mm Hg, 760 torr kPa bar mbar

6 Atmospheric Pressure: isobars in hPa General Chemistry: Chapter 6Slide 6 of 41

7 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 7 of 41 Manometers

8 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 8 of Simple Gas Laws, Isotherm: T=const Boyle 1662 P ~ 1 V PV = constant T=const

9 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 9 of 41 Example 5-6 Relating Gas Volume and Pressure – Boyles Law. P 1 V 1 = P 2 V 2 V2 =V2 = P1V1P1V1 P2P2 = 694 L V tank = 644 L

10 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 10 of 41 Charless Law, Isobar, P=const Charles 1787 Gay-Lussac 1802 V ~ T V = b T

11 Prentice-Hall © 2002General Chemistry: Chapter 6Slide 11 of 41 STP Gas properties depend on conditions. Define standard temperature and pressure (STP). International Union of Pure and Applied Chemistry (IUPAC): Temperature Absolute pressure Publishing or establishing entity °CkPa 0100IUPAC (present definition) IUPAC (former definition), NIST, ISO EPA, NIST EPA

12 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 12 of 41 Avogadros Law Gay-Lussac 1808 –Small volumes of gases react in the ratio of small whole numbers. Avogadro 1811 –Equal volumes of gases have equal numbers of molecules and –Gas molecules may break up when they react.

13 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 13 of 41 Formation of Water

14 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 14 of 41 Avogadros Law V ~ n or V = c n At STP 1 mol gas = L gas At an a fixed temperature and pressure:

15 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 15 of Combining the Gas Laws: The Ideal Gas Equation and the General Gas Equation Boyles lawV ~ 1/P Charless lawV ~ T Avogadros law V ~ n PV = nRT V ~ nT P

16 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 16 of 41 The Gas Constant R =R = PV nT = L atm mol -1 K -1 = m 3 Pa mol -1 K -1 PV = nRT = J mol -1 K -1 = m 3 Pa mol -1 K -1

17 P-V-T Surface General Chemistry: Chapter 6Slide 17 of 41

18 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 18 of 41 The General Gas Equation R =R = = P2V1P2V1 n1T2n1T2 P1V1P1V1 n1T1n1T1 = P2P2 T2T2 P1P1 T1T1 If we hold the amount and volume constant:

19 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 19 of Applications of the Ideal Gas Equation

20 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 20 of 41 Molar Mass Determination PV = nRT and n = m M PV = m M RT M = m PV RT

21 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 21 of 41 Example 6-4 Determining a Molar Mass with the Ideal Gas Equation. Polypropylene is an important commercial chemical. It is used in the synthesis of other organic chemicals and in plastics production. A glass vessel weighs g when clean, dry and evacuated; it weighs g when filled with water at 25°C (δ= g cm -3 ) and g when filled with propylene gas at mm Hg and 24.0°C. What is the molar mass of polypropylene? Strategy: Determine V flask. Determine m gas. Use the Gas Equation.

22 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 22 of 41 Example 6-4 Determine V flask : V flask = m H 2 O / d H 2 O = ( g – g) / ( g cm -3 ) Determine m gas : = g m gas = m filled - m empty = ( g – g) = cm 3 = dm 3

23 General Chemistry: Chapter 6Slide 23 of 41 Example 5-6 Example 6-4, Molar Mass with the Ideal Gas Equation Use the Ideal Gas Equation: PV = nRT PV = m M RT M = m PV RT M =M = (P kPa)( dm 3 ) ( g)( J mol -1 K -1 )(297.2 K) M = g · mol -1 P = 740.3/760 * kPa [Pa · m 3 ] = [kPa · dm 3 ] = [J]

24 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 24 of 41 Gas Densities PV = nRT and d = m V PV =PV = m M RT MP RTV m = d =, n = m M

25 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 25 of Gases in Chemical Reactions Stoichiometric factors relate gas quantities to quantities of other reactants or products. Ideal gas equation used to relate the amount of a gas to volume, temperature and pressure. Law of combining volumes can be developed using the gas law.

26 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 26 of 41 Example 6-5 Using the Ideal gas Equation in Reaction Stoichiometry Calculations. The decomposition of sodium azide, NaN 3, at high temperatures produces N 2 (g). Together with the necessary devices to initiate the reaction and trap the sodium metal formed, this reaction is used in air-bag safety systems. What volume of N 2 (g), measured at 735 mm Hg and 26°C, is produced when 70.0 g NaN 3 is decomposed. 2 NaN 3 (s) 2 Na(l) + 3 N 2 (g)

27 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 27 of 41 Example 6-5 Determine moles of N 2 : Determine volume of N 2 : n N 2 = 70 g · 1 mol NaN g · 3 mol N 2 2 mol NaN 3 = 1.62 mol N 2 = 41.1 l P nRT V = = (735 mm Hg) (1.62 mol)( J mol -1 K -1 )(299 K) 760 mm Hg kPa

28 Airbag design Prentice-Hall © 2008General Chemistry: Chapter 6Slide 28 of 41

29 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 29 of Mixtures of Gases Partial pressure –Each component of a gas mixture exerts a pressure that it would exert if it were in the container alone. Gas laws apply to mixtures of gases. Simplest approach is to use n total, but....

30 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 30 of 41 Daltons Law of Partial Pressure

31 General Chemistry: Chapter 6Slide 31 of 41 Partial pressure and volume P tot = P a + P b +… V a = n a RT/P tot and V tot = V a + V b +… VaVa V tot n a RT/P tot n tot RT/P tot = = nana n tot PaPa P tot n a RT/V tot n tot RT/V tot = = nana n tot nana = xaxa Recall

32 Average molar mass of ideal gas mixtures The average molar mass is a sum of the products of the components molar fractions (x i ) and masses (M i ).

33 The athmosphere

34 Average molar mass?

35 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 35 of 41 Pneumatic Trough P tot = P bar = P gas + P H 2 O

36 Equilibrium vapor pressure of H 2 O vs temperature Csonka,G. I. © 2008General Chemistry: Chapter 6Slide 36 of 41

37 Prentice-Hall © 2008General Chemistry: Chapter 8Slide 37 of 32 Water Vapor n H 2 O P H 2 O in air. Relative Humidity = P H 2 O (actual) P H 2 O (max) · 100%

38 Relative humidity map General Chemistry: Chapter 6Slide 38 of 41Csonka,G. I. © 2013

39 Prentice-Hall © 2008General Chemistry: Chapter 8Slide 39 of 32 Chemicals from the Atmosphere

40 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 40 of Kinetic Molecular Theory Particles are point masses in constant, random, straight line motion. Particles are separated by great distances. Collisions are rapid and elastic. No force between particles. Total energy remains constant.

41 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 41 of 41 Pressure – Assessing Collision Forces Translational kinetic energy, Frequency of collisions, Impulse or momentum transfer, Pressure proportional to impulse times frequency

42 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 42 of 41 Pressure and Molecular Speed Three dimensional systems lead to: u m is the modal speed u av is the simple average u rms

43 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 43 of 41 Pressure Assume one mole: PV=RT so: N A m = M: Rearrange:

44 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 44 of 41 Distribution of Molecular Speeds

45 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 45 of 41 Determining Molecular Speed

46 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 46 of 41 Temperature Modify: PV=RT so: Solve for e k : Average kinetic energy is directly proportional to temperature!

47 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 47 of Gas Properties Relating to the Kinetic-Molecular Theory Diffusion –Net rate is proportional to molecular speed. Effusion –A related phenomenon.

48 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 48 of 41 Grahams Law Only for gases at low pressure (natural escape, not a jet). Tiny orifice (no collisions) Does not apply to diffusion. Ratio used can be: –Rate of effusion (as above) –Molecular speeds –Effusion times –Distances traveled by molecules –Amounts of gas effused.

49 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 49 of Real Gases Compressibility factor PV/nRT = 1 – Ideal gas Deviations occur for real gases. –PV/nRT > 1 - molecular volume is significant. –PV/nRT < 1 – intermolecular forces of attraction. The green molecule is attracted by the red molecules.

50 Csonka, G. I. © 2008General Chemistry: Chapter 6Slide 50 of 41 Real Gases, Isotherms

51 Compression factor, Z Product of pressure (P) and molar volume (V m ) divided by the gas constant (R) and thermodynamic temperature (T). For an ideal gas it is equal to 1. As n = 1 Csonka, G. I. © 2008General Chemistry: Chapter 6Slide 51 of 41

52 GasV m (dm 3 ) He Ne H2H CO H2OH2O Real gases at STP P 0 and T = 0 C° Csonka, G. I. © 2008

53 General Chemistry: Chapter 6Slide 53 of 41 van der Waals Equation van der Waals Coefficients Gasa (Pa m 6 /mol 2 )b(m 3 /mol) Helium · Neon · Hydrogen · Carbon dioxide · Water vapor · CH · 10 -6

54 van der Waals vs ideal curves Csonka, G. I. © 2008General Chemistry: Chapter 6Slide 54 of 41

55 Prentice-Hall © 2008General Chemistry: Chapter 6Slide 55 of 41 Chapter 6 Questions 9, 13, 18, 31, 45, 49, 61, 63, 71, 82, 85, 97, 104.


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