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Exploring Gas Laws: Boyle’s, Charles’s, and Gay-Lussac’s Equations

Understand how pressure, volume, and temperature affect gases with examples and calculations of Boyle’s Law, Charles’s Law, and Gay-Lussac’s Law. Learn the principles of the Kinetic Molecular Theory and ideal gases.

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Exploring Gas Laws: Boyle’s, Charles’s, and Gay-Lussac’s Equations

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  1. Gas Laws

  2. 1. Kinetic Molecular Theory • Ideal Gases : • Gas particles do not attract or repel each other. • Gas particles are much smaller than the distances between them. They are mostly empty space. • Gas particles are in constant, random motion. • No kinetic energy is lost when gas particles collide with each other or with the walls of their container.

  3. All gases have the same average kinetic energy at a given temperature. (note not the same velocity!) • Real gases behave like ideal gases except at high pressures and low temperatures. • At high pressures or low temperatures the particles are closer together and are effected by the intermolecular forces.

  4. Temperature – average kinetic energy of the gas particles. • Gas laws require temperature to be in units of Kelvin. • No negative temperatures • Does not have zero as a temperature except at absolute zero. • Kelvin = 273 + ºC • 0ºC = 273 K • 100ºC = 373 K • 26ºC = 299 K • 379 K = 106ºC • 318 K = 45ºC

  5. STP – standard temperature and pressure • 0ºC, 1 atm • 0ºC, 101.3 kPa • 273 K, 760 mmHg • 273 K, 101.3 kPa • Gases are described by the : • Number of molecules (moles) • Pressure • Temperature • Volume

  6. 2. Boyle’s Law • The volume of a given amount of gas, held at constant temperature varies inversely with the pressure. • Constant temperature, constant number of particles. • Pressure ↑ Volume ↓ (inverse relationship) • Pressure ↓ Volume ↑ • PV = constant

  7. When collecting gases in the lab, we use the technique of water displacement. • The product gases bubble into a container filled with water. • The collected gas is “wet” because it contains water vapor. • The water vapor exerts a partial pressure. • To determine the pressure exerted by the gas, you subtract the pressure of the water vapor. • The vapor pressure exerted by water depends on the temperature of the gas. • Pdry gas = Pwet gas – Pwater

  8. 3. Charles’s Law • The volume of a given amount of gas, held at constant pressure, varies directly with the Kelvin temperature. • Constant pressure, constant number of particles. • Temperature ↑ Volume ↑ (direct relationship) • Temperature ↓ Volume ↓ • Constant = • Temperature MUST be in Kelvin!

  9. 4. Gay-Lussac’s Law • The pressure of a given amount of gas, held at constant volume, varies directly with the Kelvin temperature. • Constant volume, constant number of particles. • Pressure ↑ Temperature ↑ (direct relationship) • Pressure ↓ Temperature ↓ • Constant = • Temperature MUST be in Kelvin!

  10. 5. Combined Gas Law • States the relationship among pressure, volume, and Kelvin temperature of a fixed amount of gas. • 1 = before 2 = after • Can determine the pressure, volume, or temperature should the other variables change! • Always convert temperature to Kelvin!!!!!

  11. Constant Temperature, T1 = T2 • So P1V1 = P2V2 • Constant Pressure, P1 = P2 • So • Constant Volume, V1 = V2 • So

  12. 6. Example Problems • A gas occupies a volume of 2.45 liters at a pressure of 104.3 kPa and a temperature of 20°C. What volume will the gas occupy if the pressure changes to 99.3 kPa and the temperature remains at 20°C?

  13. A 525 ml sample of hydrogen gas is collected over water at 80.0°C. The pressure of the wet hydrogen gas is 95.0 kPa. What volume will the dry hydrogen gas occupy at 101.3 kPa pressure? The vapor pressure of water at 80.0°C is 47.3 kPa.

  14. A 325 ml sample of gas is collected over water at 27°C. The pressure in the container is 68 kPa. What would the pressure be if the sample was dried and placed into a 500.0 ml container at 27°C? The vapor pressure of water at 27°C is 3.6 kPa.

  15. A tank of compressed carbon dioxide has a temperature of 23.6°C and a volume of 31.4 liters. The carbon dioxide is completely transferred into a smaller tank that has a volume of 25.0 liter. Assuming none of the carbon dioxide escapes during the transfer, what is the temperature, in °C, of the carbon dioxide in the smaller tank if the temperature is lowered to achieve the same pressure as in the large tank?

  16. The pressure in a bicycle tire is 1.34 atm at 33.0°C. At what temperature will the pressure inside the tire be 1.60 atm? Assume the volume is constant.

  17. What volume will a 8.6 liter sample of gas at 105.5 kPa, 25°C occupy at 101.3 kPa and 0°C?

  18. A gas balloon is sitting in the freezer at -5°C, 3.25 liters, and a pressure of 102.1 kPa. The balloon is moved to the counter where the temperature is 28°C and the pressure is 100.8 kPa. What is the volume of the balloon after sitting on the counter several hours?

  19. Hydrogen gas at a temperature of 22.0°C that is confined in a 5.00 L cylinder exerts a pressure of 4.20 atm. What is the volume of the gas at STP?

  20. Homework Gas Laws

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