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Gases

Gases. Chapter 10 BLB 12 th. Expectations. Convert between different pressure units. Gas Laws: s olve for any gas quantity from other given quantities. Include gases in stoichiometric calculations. Work with mole fractions and partial pressures.

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Gases

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  1. Gases Chapter 10 BLB 12th

  2. Expectations Convert between different pressure units. Gas Laws: solve for any gas quantity from other given quantities. Include gases in stoichiometric calculations. Work with mole fractions and partial pressures. Calculate and compare the average velocities of gases.

  3. 10.1 Characteristics of Gases • Earth’s Atmosphere - dry air near sea level (from 18.1, p. 751) • Other common gases (Table 10.1, p. 384)

  4. Characteristics of Gases, cont. • 3 states of matter: solid, liquid, gas • Properties of gases: • Gases expand to fill a container. • Gases are highly compressible. • Gases mix readily and completely mix with other gases. • Gases exert pressure on their surroundings. • All gases behave similarly regardless of identity.

  5. Characteristics of Gases, cont. In order to fully describe a gas, four quantities are needed: • Pressure (P) – in Pa (SI unit), atm, mm Hg, torr • Volume (V) – in L • Temperature (T) – in K • Quantity of gas (n) – in moles

  6. 10.2 Pressure • P = F/A • Measuring pressure: • Atmospheric pressure – measured with a barometer. (p. 386) • Gas pressure in a container – measured with a manometer. (p. 387) • Standard atmospheric pressure = 1 atm 1 atm = 760 torr = 760 mm Hg= 29.92 in Hg = 101,325 Pa = 14.70 psi = 1013.25 mBar

  7. Barometer Manometer

  8. Pressure Conversions

  9. 10.4 The Ideal-Gas Equation • A gas which obeys this equation is said to behave ideally.

  10. Ideal-Gas Equation, cont. • There are no ideal gases. • A real gas approaches ideal behavior at low pressures and high temperatures, where molecules can behave (almost) independently. (section 10.9) • Standard temperature & pressure (STP) T = 0°C (273.15 K) P = 1 atm

  11. Molar Volume • Of an ideal gas at STP? • Of a real gas?

  12. Calculate the following for a sample of Cl2 gas with a volume of 9.22 L at 1124 torr and 24°C. • Mass of Cl2? • Volume (in L) at STP?

  13. Cont. Cl2gas with a volume of 9.22 L at 1124 torr and 24°C. • At what temperature will V = 15.00 L if P = 876 torr? • At what pressure will V = 6.00 L if T = 58°C

  14. 10.3 The [Other] Gas Laws

  15. Boyle’s Law

  16. Boyle’s Law for Real Gases

  17. Charles’s Law & Absolute Zero

  18. Charles’s Law for Real Gases

  19. Avogadro’s Law: Equal volumes of gases at the same T and P contain equal numbers of molecules.

  20. A sample of gas occupiesa volume of 1248 ft3 at 0.988 atm and 28.0°C. • Calculate the pressure if volume is decreased to 978 ft3 at constant T. • At what temperature in °C is the volume 1435 ft3 at constant P?

  21. 10.30 Nitrogen and hydrogen gases react to form ammonia gas: N2(g) + 3 H2(g) → 2 NH3(g). At a certain temperature and pressure, 1.2 L of N2 reacts with 3.6 L of H2. If all the N2 and H2 are consumed, what volume NH3 will be produced?

  22. 10.5 Further Applications of PV=nRT • Gas Densities and Molar Mass (M) density (g/L) molar mass (g/mol)

  23. Calculate the density of SF6 at 455 torr and 32°C.

  24. Calculate the molar mass of a vapor that has a density of 6.345 g/L at 22°C and 743 torr.

  25. Gas Stoichiometry • Use gas information to obtain moles. • Otherwise, standard stoichiometry guidelines apply.

  26. 10.58 Calcium hydride, CaH2, reacts with water to form hydrogen gas. How many grams of CaH2 are needed to generate 64.5 L of H2 gas if the pressure of H2 is 814 torr at 32°C?CaH2(s) + 2 H2O(l) → Ca(OH)2(aq) + 2 H2(g)

  27. 10.6 Gas Mixtures and Partial Pressures • For a fixed-volume container: pressures and moles are additive; volume is fixed. • Dalton’s Law of Partial Pressure • Collecting gases over water:

  28. Collection of a gas over water Total gas collected = product gas + water vapor Ptotal = Pgas+ Pwater

  29. Acetylene gas, C2H2(g), can be prepared by the reaction of calcium carbide with water. Calculate the volume of C2H2 that is collected over water at 21°C by reaction of 3.26 g of CaC2 if the total pressure of the gas is 748 torr? The vapor pressure of water at 21°C is 18.65 torr.CaC2(s) + 2 H2O(l) → Ca(OH)2(aq) + C2H2(g)

  30. Gas Mixtures, cont. • Mole fraction (X) – ratio of moles of one substance to the total number of moles in mixture.

  31. A mixture of gases contains 0.75 mol N2, 0.30 mol O2, and 0.15 mol CO2. If the total pressure of the mixture is 1.56 atm, what is the partial pressure of each component?

  32. 5.25 g of SO2(g) and 2.35 g of N2(g) are placed into a 13.6-L container at 25°C.(a) What is the PSO2?(b) What is the PN2? (c) What is the Ptotal?

  33. 10.7 Kinetic-Molecular Theory of Gases Postulates: (pp. 403) • Particles are in constant, random motion. • Particles are so small … that the volume of each is negligible relative to the total volume. • Attractive and repulsive forces between particles are negligible. • Energy can be transferred between particles; average kinetic energy is constant. • Average kinetic energy is directly proportional to the absolute temperature. At a given T all gas particles have same average kinetic energy.

  34. Molecular Speeds for N2 Root-mean-square speed

  35. Molecular Speeds of Different Gases at 25°C

  36. Molecular Speed • Average kinetic energy is the same for any gas at a given T. ► But the mass of each gas is different.◄ • Root-mean-square speed depends on mass and T. • Lighter molecules move faster. • Heavier molecules move more slowly.

  37. 10.77 (a) Order the following based on average molecular speed at 25°C: Ne, HBr, SO2, NF3, CO(b) Calculate the rms speed of NF3 at 25°C.

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