1 / 57

Molecular Composition of Gases

Molecular Composition of Gases. Chapter 11. Gay-Lussac’s law of combining volumes of gases. At constant temperature and pressure, the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers. Example.

betsy
Télécharger la présentation

Molecular Composition of Gases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Molecular Composition of Gases Chapter 11 Chemistry Chapter 11

  2. Gay-Lussac’s law of combining volumes of gases • At constant temperature and pressure, the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers Chemistry Chapter 11

  3. Example • When 2 L of hydrogen react with 1 L of oxygen 2 L of water vapor are produced. • Write the balanced chemical equation: Chemistry Chapter 11

  4. You try • When 1 L of hydrogen gas reacts with 1 L of chlorine gas, 2 L of hydrogen chloride gas are produced. • Write the balanced chemical equation: Chemistry Chapter 11

  5. Avogadro's Law • Equal volumes of gases at the same pressure and temperature contain the same number of molecules • Atoms can’t split  diatomic molecules • Gas volume is proportional to the number of molecules Chemistry Chapter 11

  6. Molar Volume • 1 mole of any gas contains 6.022 x 1023 molecules. • According to Avogadro’s law, 1 mole of any gas must have the same volume. • Standard molar volume: volume of 1 mole of any gas at STP • 22.4 L Chemistry Chapter 11

  7. Example • You are planning an experiment that requires 0.0580 mol of nitrogen monoxide gas. What volume in liters is occupied by this gas at STP? • 1.30 L NO Chemistry Chapter 11

  8. You try • A chemical reaction produces 2.56 L of oxygen gas at STP. How many moles of oxygen are in this sample? • 0.114 mol O2 Chemistry Chapter 11

  9. Example • Suppose you need 4.22 g of chlorine gas. What volume at STP would you need to use? • 1.33 L Cl2 Chemistry Chapter 11

  10. You try • What is the mass of 1.33 x 104 mL of oxygen gas at STP? • 19.0 g O2 Chemistry Chapter 11

  11. Discuss • Explain Gay-Lussac’s law of combining volumes • State Avogadro’s law and explain its significance. Chemistry Chapter 11

  12. Review • Boyles Law: • Charles Law: • Avogadro’s Law: Chemistry Chapter 11

  13. Math • A quantity that is proportional to each of several quantities is also proportional to their product. Therefore: Chemistry Chapter 11

  14. More math • Convert a proportionality • to an equality by multiplying by a constant Chemistry Chapter 11

  15. Therefore • We can covert • to Chemistry Chapter 11

  16. More neatly Chemistry Chapter 11

  17. This means…. • The volume of a gas varies directly with the number of moles and the temperature in Kelvin. • The volume varies indirectly with pressure. Chemistry Chapter 11

  18. What if… • n and T are constant? • nRT is a constant, k • Boyle’s Law • n and P are constant? • nR/P is a constant, k • Charles’s Law Chemistry Chapter 11

  19. What if… • P and T are constant? • RT/P is a constant, k • Avogadro’s law Chemistry Chapter 11

  20. The ideal gas constant • R • Value depends on units • SI units: Chemistry Chapter 11

  21. Other units Chemistry Chapter 11

  22. Solving ideal gas problems • Make sure the R you use matches the units you have. • Make sure all your units cancel out correctly. Chemistry Chapter 11

  23. Example • A 2.07 L cylinder contains 2.88 mol of helium gas at 22 °C. What is the pressure in atmospheres of the gas in the cylinder? • 33.7 atm Chemistry Chapter 11

  24. You try • A tank of hydrogen gas has a volume of 22.9 L and holds 14.0 mol of the gas at 12 °C. What is the reading on the pressure gauge in atmospheres? • 14.3 atm Chemistry Chapter 11

  25. Example • A reaction yields 0.00856 mol of oxygen gas. What volume in mL will the gas occupy if it is collected at 43 °C and 0.926 atm pressure? • 240. mL Chemistry Chapter 11

  26. You try • A researcher collects 9.09 x 10-3 mol of an unknown gas by water displacement at a temperature of 16 °C and 0.873 atm pressure (after the partial pressure of the water vapor has been subtracted). What volume of gas in mL does the researcher have? • 247 mL Chemistry Chapter 11

  27. Finding mass • Number of moles (n) equals mass (m) divided by molar mass (M). Chemistry Chapter 11

  28. Example • What mass of ethene gas, C2H4, is contained in a 15.0 L tank that has a pressure of 4.40 atm at a temperature of 305 K? • 74.0 g Chemistry Chapter 11

  29. You try • NH3 gas is pumped into the reservoir of a refrigeration unit at a pressure of 4.45 atm. The capacity of the reservoir is 19.4 L. The temperature is 24 °C. What is the mass of the gas in kg? • 6.03 x 10-2 kg Chemistry Chapter 11

  30. Example • A chemist determines the mass of a sample of gas to be 3.17 g. Its volume is 942 mL at a temperature of 14 °C and a pressure of 1.09 atm. What is the molar mass of the gas? • 72.7 g/mol Chemistry Chapter 11

  31. Density Chemistry Chapter 11

  32. You try • The density of dry air at sea level (1 atm) is 1.225 g/L at 15 °C. What is the average molar mass of the air? • 29.0 g/mol Chemistry Chapter 11

  33. Stoichiometry • Involves mass relationships between reactants and products in a chemical reaction • For gases, the coefficients in the balanced chemical equation show volume ratios as well as mole ratios • All volumes must be measured at the same temperature and pressure Chemistry Chapter 11

  34. Volume-Volume calculations • From volume of one gas to volume of another gas • Use volume ratios just like mole ratios in chapter 9 Chemistry Chapter 11

  35. Example • Xenon gas reacts with fluorine gas to produce the compound xenon hexafluoride, XeF6. Write the balanced equation for this reaction. • Xe(g) + 3F2(g)  XeF6(g) • If a researcher needs 3.14 L of XeF6 for an experiment, what volumes of xenon and fluorine should be reacted? • 3.14 L of Xe and 9.42 L of F2 Chemistry Chapter 11

  36. Example • Nitric acid can be produced by the reaction of gaseous nitrogen dioxide with water.3NO2(g) + H2O(l)  2HNO3(l) + NO(g) • If 708 L of NO2 gas react with water, what volume of NO gas will be produced? • 236 L Chemistry Chapter 11

  37. You try • What volume of hydrogen gas is needed to react completely with 4.55 L of oxygen gas to produce water vapor? • 9.10 L Chemistry Chapter 11

  38. You try • At STP, what volume of oxygen gas is needed to react completely with 2.79 x 10-2 mol of carbon monoxide gas, CO, to form gaseous carbon dioxide? • 0.312 L Chemistry Chapter 11

  39. You try • Fluorine gas reacts violently with water to produce hydrogen fluoride and ozone according to the following equation:3F2(g) + 3H2O(l)  6HF(g) + O3(g) • What volumes of O3 and HF gas would be produced by the complete reaction of 3.60 x 104 mL of fluorine gas? • 1.20 x 104 mL O3 and 7.20 x 104 mL HF Chemistry Chapter 11

  40. You try • Ammonia is oxidized to make nitrogen monoxide and water4NH3(g) + 5O2(g)  4NO(g) + 6H2O(l) • At STP, what volume of oxygen will be used in a reaction of 125 mol of NH3? What volume of NO will be produced? • 3.50 x 103 L O2 and 2.80 x 103 L NO Chemistry Chapter 11

  41. Volume-mass and mass-volume • Converting from volume to mass or from mass to volume • Must convert to moles in the middle • Ideal gas law may be useful for finding standard conditions Chemistry Chapter 11

  42. Example • Aluminum granules are a component of some drain cleaners because they react with sodium hydroxide to release both heat and gas bubbles, which help clear the drain clog. The reaction is:2NaOH(aq) + 2Al(s) + 6H2O (l)  2NaAl(OH)4(aq) + 3 H2(g) • What mass of aluminum would be needed to produce 4.00 L of hydrogen gas at STP? • 3.21 g Chemistry Chapter 11

  43. Example • Air bags in cars are inflated by the sudden decomposition of sodium azide, NaN3 by the following reaction:2NaN3(s)  3N2(g) + 2Na(s) • What volume of N2 gas, measured at 1.30 atm and 87 °C, would be produced by the reaction of 70.0 g of NaN3? • 36.6 L Chemistry Chapter 11

  44. You try • What volume of chlorine gas at 38°C and 1.63 atm is needed to react completely with 10.4 g of sodium to form NaCl? • 3.54 L Cl2 Chemistry Chapter 11

  45. Example • A sample of ethanol burns in O2 to form CO2 and H2O according to the following reaction.C2H5OH + 3O2 2CO2 + 3H2O • If the combustion uses 55.8 mL of oxygen measured at 2.26 atm and 40.°C, what volume of CO2 is produced when measured at STP? • 73.3 mL CO2 Chemistry Chapter 11

  46. You try • Dinitrogen pentoxide decomposes into nitrogen dioxide and oxygen. If 5.00 L of N2O5 reacts at STP, what volume of NO2 is produced when measured at 64.5 °C and 1.76 atm? • 7.02 L NO2 Chemistry Chapter 11

  47. Review • Diffusion: the gradual mixing of gases due to their random motion • Effusion: gases in a container randomly pass through a tiny opening in the container Chemistry Chapter 11

  48. Rate of effusion • Depends on relative velocities of gas molecules. • Velocity varies inversely with mass • Lighter particles move faster Chemistry Chapter 11

  49. Kinetic energy • Depends only on temperature • Equals • For two gases, A and B, at the same temperature • Each M stands for molar mass Chemistry Chapter 11

  50. Algebra time Chemistry Chapter 11

More Related