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Chapter 10- Gases

Chapter 10- Gases. What are the characteristics of gases? Variable shape Variable volume The atmosphere is composed of gases. The two major components are nitrogen(78%) and oxygen(21%). Kinetic Molecular Theory. A theory that explains the behavior of gases at the molecular level

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Chapter 10- Gases

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  1. Chapter 10- Gases • What are the characteristics of gases? • Variable shape • Variable volume • The atmosphere is composed of gases. The two major components are nitrogen(78%) and oxygen(21%).

  2. Kinetic Molecular Theory • A theory that explains the behavior of gases at the molecular level • Based on the Ideal Gasa gas for which the product of the pressure and volume is proportional to the absolute temperature • If a gas is moving it has energyKinetic Energy • KE=1/2mv2

  3. Four Variables describe a Gas • 1. Temperature • Based on absolute temperatureKelvin How do we convert to Kelvin? K=°C + 273

  4. Cont. • 2. Volume • V= l•w•h • Common units are L, ml, or cm3 • 3. Pressure • - force exerted over an area • P=Force/area • Force is measured in Newtons(N) • Area is measured m2 or other similar units

  5. Pressure cont. • How is pressure measured? • Barometer- device used to measure atmospheric pressure • What are the units of Pressure? • A. Millimeters of mercury(mm Hg) • 1mm of Hg= 1 torr • Atmospheric pressure at sea level at 0° C is 760 mm

  6. Pressure cont. • B. Atmosphere of pressure(atm) • 1 atm= 760 mm Hg • Pascal(Pa) – the pressure exerted by a force of one newton acting on an area of one square meter. 1atm= 1.01325 x 105 Pa or 101.325 kPa

  7. Standard Temperatureand Pressure • To compare volumes of gases, it is necessary to know the temperature and pressure at which the volumes are measured. • The standard conditions are called Standard Temperature and Pressure(STP) • STP= 0°C and 1.0000atm

  8. 4. Number of moles(n) • The volume of one mole of gas at STP is called Molar Volume.

  9. The Gas Laws • 1. Charles’s Law • -the volume of a gas at constant pressure is directly proportional to the temperature. • V1/T1=V2/T2

  10. Example of Charles’s Law • A sample of gas occupies 24 m3 at 100. K. What volume would the gas occupy at 400.K? • What do you know? • V1=24 m3 • T1=100. K • T2= 400. K • V2= ?

  11. Boyle’s Law • The volume of a gas at constant temperature is inversely proportional to the pressure. • P1V1=P2V2

  12. Example of Boyle’s Law • The gas in a balloon has a volume of 4 L at 100 kPa. The balloon is released into the atmosphere, and the gas in it expands to a volume of 8 L. What is the pressure on the balloon at the new volume? • What do you know? • V1= 4 L P1= 100 kPa • V2= 8 L P2 = ?

  13. Gay-Lussac’s Law • The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature. • P1/T1=P2/T2 • The gas in a container is at a pressure of 3.00 atm at 25°C. Directions on the container warn the user not to keep it in a place where the temp. exceeds 52°C. What would the gas pressure in the container be at 52°C?

  14. Dalton’s Law of Partial Pressures • For a mixture of gases in a container the total pressure exerted is the sum of the pressures that each gas would exert if it were alone. • PTotal = P1 + P2 + P3 + …

  15. Example • Hydrogen gas is collected over water at a total pressure of 95.0 kPa. The volume of hydrogen collected is 28 ml at 25° C. If the pressure of water vapor at 25° C is 3.17 kPa, what is the partial pressure of hydrogen gas?

  16. Graham’s Law Diffusion- movement of particles from regions of high density to regions of low density Example: smelling food throughout the house Effusion- passage of a gas under pressure through a tiny opening Example: a helium balloon is buoyant at first but later hangs toward the ground because helium has escaped through holes in the balloon

  17. Con. • Graham’s Law- the ratio of the rates of effusion(diffusion) of two gases is equal to the square root of the inverse of their molar masses or densities • Rate1/Rate2= M2/M1

  18. Example • An oxygen molecule travels at about 480 m/s at room temperature. How fast would a molecule of sulfur trioxide travel at the same temperature?

  19. Combined Gas Law • Expresses the relationship between pressure, volume, and temperature of a fixed amount of gas. • P1V1= P2V2 • T1 T2

  20. Example of Combined Gas Law • A helium balloon with a volume of 410. mL is cooled from 27° C to -27° C. The pressure on the gas is reduced from 110. kPa to 25 kPa. What is the volume of the gas at the lower temperature and pressure? • What do you know? • V1= 410. mL V2= ? P1= 110. kPa P2= 25. kPa • T1= 27°C= 300 K T2= -27°= 246 K

  21. Ideal Gas Law • Is the mathematical relationship among pressure, volume, temperature, and the number of moles of a gas. • PV= nRT • P = pressure • V=Volume • n= number of moles • T= temperature • R=8.314 L•kPa • mol•K

  22. Example of Ideal Gas Law • A sample of carbon dioxide with a mass of .250 g was placed in a 350 ml container at 400. K. What is the pressure exerted by the gas? • What do you know? • V= 350 ml • T= 400. K • M= .250 g of carbon dioxide • P= ?

  23. Ideal gas and Stoichiometry • How many liters of hydrogen gas will be produced at 280. K and 96.0 kPa if 40.0 g of sodium react with excess hydrochloric acid according to the following equation? • 2Na(s) + 2HCl(aq) 2NaCl(aq) + H2(g)

  24. What do we know? • P= 96.0 kPa • R= 8.314 L•kPa/mol•K • T= 280. K • N= calculate with molar mass and mole ratio • V=?

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