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Gases

Gases. Chapters 12.1 and 13. 12.1 Main Idea. Gases expand, diffuse, exert pressure, and can be compressed because they are in a low-density state consisting of tiny, constantly moving particles. Objectives. Predict the behavior of gases using the kinetic-molecular theory

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Gases

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  1. Gases Chapters 12.1 and 13

  2. 12.1 Main Idea Gases expand, diffuse, exert pressure, and can be compressed because they are in a low-density state consisting of tiny, constantly moving particles

  3. Objectives • Predict the behavior of gases using the kinetic-molecular theory • Explain how mass affects the rates of diffusion and effusion • Calculate the partial pressure of a gas • Measure gas pressure

  4. Review Vocabulary • Kinetic energy • Molar mass

  5. New Vocabulary • Kinetic-molecular theory • Elastic collision • Temperature • Diffusion • Graham’s Law • Pressure • Barometer • Manometer • Pascal (Pa) • Dalton's law of partial pressure • Atmosphere (atm)

  6. Kinetic-Molecular (KM) Theory • Assumptions • Particle size is very small • Particles take up relatively no space • Particles are far apart • Very little interaction of particles • Collisions are elastic • No kinetic energy is lost in a collision

  7. Particle Energy • Determined by mass and velocity • Temperature- the average kinetic energy of particles in matter

  8. Behavior of Gases • Pressure- gases will expand to fill the space they occupy

  9. Behavior of Gases • Compression and expansion- density of material can be changed by changing the available volume

  10. Behavior of Gases • Diffusion- movement of one material through another • Concentration gradient • Effusion- gas escaping from a confined space through tiny openings

  11. What is the ratio of the rate of diffusion for ammonia and hydrogen chloride?

  12. Calculate the ratio of effusion rates for nitrogen gas and neon • RH/RHe=0.849

  13. Pressure • Pressure (P) is defined as the force per unit area on a surface. (P=F/A) • Gas pressure is caused by collisions of the gas molecules with each other and with surfaces with which they come into contact. • The pressure exerted by a gas depends on volume, temperature, and the number of molecules present. • The greater the number of collisions of gas molecules, the higher the pressure will be.

  14. Gas Pressure Barometer Manometer Manometers measure gas pressure in a closed system • Barometers measure atmospheric pressure • open system

  15. Gas Pressure • Units • Pascal (1 Pa = 1 /m2) • Atmosphere (1 atm = 101.3 kPa) • mm Hg (1 atm = 760 mm Hg) • Torr(1 torr = 1 mm Hg)

  16. Dalton’s Law of Partial Pressures • total pressure is the sum of the partial pressures • Ptot=P1 + P2 + P3 + … Pn

  17. A mixture of O2, CO2 and N2 has a total pressure of 0.97 atm. What is the partial pressure of O2 if the partial pressure of CO2 is 0.70 atm and the partial pressure of N2 is 0.12 atm? • 0.97 atm = 0.70 atm + 0.12 atm + x • X = 0.15 atm

  18. Can you… • Predict the behavior of gases using the kinetic-molecular theory • Explain how mass affects the rates of diffusion and effusion • Calculate the partial pressure of a gas • Measure gas pressure

  19. The Gas Laws Chapter 13.1

  20. 13.1 Main Idea For a fixed amount of gas, a change in one variable- pressure, volume or temperature- affects the other two.

  21. 13.1 Objectives • State the relationships among pressure, volume, temperature, and the amount of gas • Apply gas laws to problems involving pressure, volume, temperature, and the amount of gas • Create graphs of the relationships among pressure, volume, temperature, and the amount of gas • Solve problems related to fixed amounts of gases

  22. Review Vocabulary • Scientific law • Directly related • Indirectly (inversely) related • Kelvin

  23. New Vocabulary • Ideal gas • Absolute zero • Boyle’s law • Charles’s law • Gay-Lussac’s law • Combined gas law

  24. Ideal gas • Non-existent, but assumes the following: • Completely elastic collisions • Particles occupy no volume • Large number of particles • No attractive or repellent forces between particles • Molecules are in completely random motion

  25. Boyle’s Law • Constants: amount of gas (n) and temperature (T) • Boyle's Law in Motion

  26. A diver blows a 0.75 L air bubble 10 m under water. As it rises, the pressure goes from 2.25 atm to 1.03 atm. What is the volume of the bubble at the surface? • P1V1=P2V2 2.25 atm 0.75 L = 1.6 L 1.03 atm

  27. Charles’s Law • Constants: amount of gas (n) and pressure (P) • Temperature is in Kelvin (K) • K= C + 273.0 • Charles' Law in Motion

  28. A helium balloon in a closed car occupies a volume or 2.32 L at 40°C.If the temperature rises to 75°C, what is the new volume of the balloon? • V2=V1T2/T1 348.0 K 2.32 L = 2.58 L 313.0 K

  29. Gay-Lussac’s Law • Constants: amount of gas (n) and volume (V) • T must be in Kelvin • Gay-Lussac in Motion

  30. The pressure of oxygen gas inside a canister is 5.00 atm at 25°C. the canister is placed in a cold environment where the temperature is -10°C; what is the new pressure in the canister? • P2=P1T2/T1 263.0 K 5.00 atm = 4.41 atm 298.0 K

  31. Predict • The relationship between pressure and amount of gas at a fixed temperature and volume • Pressure-Moles relationship • The relationship between volume and the amount of gas at a fixed temperature and amount of gas • Volume-Moles relationship

  32. Combined Gas Law • Combination of Boyle’s, Charles’, and Gay-Lussac’s laws

  33. A gas at 110 kPa and 30.0°C fills a flexible container with an initial volume of 2.00L. If the temperature is raised to 80.0°C and the pressure increases to 440 kPa, what is the new volume? • 0.58 L

  34. Gas Law Summary

  35. Can you… • State the relationships among pressure, volume, temperature, and the amount of gas • Apply gas laws to problems involving pressure, volume, temperature, and the amount of gas • Create graphs of the relationships among pressure, volume, temperature, and the amount of gas • Solve problems related to fixed amounts of gases

  36. Ideal Gas Law 13.2

  37. 13.2 Main Idea The ideal gas law relates the number of particles to pressure, temperature, and volume

  38. 13.2 Objectives • Relate the number of particles and volume using Avogadro’s principle • Relate the amount of gas present to its pressure, temperature, and volume using the ideal gas law • Compareandcontrast the properties of real gases and ideal gases • Solve problems using the ideal gas law

  39. Review Vocabulary • Mole • Molar mass (M)

  40. New Vocabulary • STP • Avogadro’s principle • Molar volume • Ideal gas constant (R) • Ideal gas law

  41. STP • Standard temperature and pressure • Standard temperature • 0.00000°C = 273.15 K • Standard pressure • 1 atm = 760 torr = 101.325 kPa

  42. Avogadro’s Principle • Equal volumes of (ideal) gases, at the same temperature and pressure, contain equal numbers of particles • 1 mol gas = 22.4 L at STP

  43. How much volume do the following gases fill at STP 1 mol CH4 1 mol CO2 1 mol H2O 1 mol Ne 2 mol He 1 mol O2

  44. Molar Volume • The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 kg of methane will occupy at STP. • M = m/n • M = molar mass • m = mass • n = number of moles

  45. The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 kg of methane will occupy at STP. • Molar mass (M) = 16.05 g/mol (C + 4H)

  46. The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 kg of methane will occupy at STP. • Molar mass (M) = 16.05 g/mol (C + 4H) • Number of moles (n) = ?? • M = m/n • n = m/M 2000 g CH4 1 mol = 125 mol 16.05 g

  47. The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 kg of methane will occupy at STP. • Molar mass (M) = 16.05 g/mol (C + 4H) • Number of moles (n) = 125 mol 2000 g CH4 1 mol = 125 mol 16.05 g

  48. The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 kg of methane will occupy at STP. • Molar mass (M) = 16.05 g/mol (C + 4H) • Number of moles (n) = 125 mol • Molar volume = ?? 125 mol 22.4 L = 2800 L 1 mol

  49. Ideal Gas Law • PV=nRT • P = pressure (atm) • V = volume (L) • n = number of moles of gas (mol) • R = gas constant (L•atm)/(mol•K) • T = temperature (K)

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