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GASES

GASES. Chemistry 2011. Characteristics of Gases. Fill their containers completely Have mass Can be compressed Exert pressure Mix rapidly. Kinetic Molecular Theory. A simple model to explain the properties of gases Assumptions:

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GASES

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  1. GASES Chemistry 2011

  2. Characteristics of Gases • Fill their containers completely • Have mass • Can be compressed • Exert pressure • Mix rapidly

  3. Kinetic Molecular Theory • A simple model to explain the properties of gases • Assumptions: • The volume of the individual gas particles is insignificant (zero). • The particles are in constant random motion. Perfectly elastic collisions. (no loss of energy) • The particles exert no forces (repulsion or attraction) on each other • The average kinetic energy is directly proportional to it’s temperature in Kelvin.

  4. Kinetic Energy • Kinetic energy depends on temperature KE = 3/2 RT • Kinetic energy is also dependent on mass and velocity of particles, KE = mv2/2

  5. Measuring Gases Four Variables to describe a gas • Pressure • Volume • Temperature • Number of particles

  6. Pressure • The amount of force exerted by gas molecules hitting the walls of their container • Force per unit area • Typical units atm, mm Hg, torr, kPa, psi • Conversions 1 atm = 760 mm Hg = 760 torr = 101.3 kPa = 14.7 psi

  7. Manometer and Barometers • Manometers measure gas pressure. • Barometers measure atmospheric pressure.

  8. 1. If atmospheric pressure is 753 mm Hg, what is the pressure of the gas in this manometer? Express your answer in atmospheres.

  9. If atmospheric pressure is 0.955 atm, what is the pressure of the gas in this manometer? Express your answer in atmospheres.

  10. Homework – Copy and CompleteExpress your answers in atm.

  11. Do Now: • Turn in your homework • Complete pg 390 #25-28

  12. Manometer answers • 0.957 atm • 0.901 atm • 1.146 atm • 0.993 atm • 0.984 atm • 0.0657 atm

  13. Temperature and Kinetic Theory • Temperature is the measure of the average kinetic energy of the particles in a substance. • KE = 1 mv2 or KE = 3 RT 2 2

  14. Heat ≠ Temperature • Heat is the amount of energy transferred from a hotter object to a cooler object. • Heat is measured in Joules

  15. Boyle’s Law

  16. Boyle’s Law • At constant temperature, pressure and volume of a gas are inversely related. • Mathematically, P1V1 = P2V2 Where, P1 = Pressure at one state (initial), V1 = Volume at one state (initial), P2 = Pressure at another state (final), V2 = Volume at another state (final)

  17. Charles’ Law

  18. Charles’ Law • If the amount and pressure of a gas are constant, the volume of the gas is directly proportional to temperature in Kelvin. • Mathematically, V1 = V2 T1 T2

  19. Guy – Lussac’s Law • If the amount and volume of gas are constant, pressure is directly proportional to temperature. • Mathematically, P1 = P2 T1 T2

  20. Combined Gas Law

  21. Avogadro’s Law • If pressure and temperature are constant, volume is directly proportional to the amount (moles) of gas. • Mathematically, V1 = V2 n1 n2

  22. New combined gas law • Combines all four gas laws. • Anything that is held constant when changing conditions gets crossed out.

  23. Ideal Gas Law • Combines all four variables of the gas, pressure, temperature, amount, and volume. PV = nRT • Where, P = pressure in kPa or atm V = volume in Liters n = moles of gas R = Universal Gas constant (0.08206 L· atm/K·mol or 8.31 L·kPa/K·mol) T = Temperature in Kelvin

  24. Using the ideal gas law • When a particular gas is at one state. No changes in any of the conditions • When you know three of the four variables, you can solve for the 4th. • Example, Calculate the volume of 3.00 mol H2 at 24oC and 100.5 kPa. 73.7 L H2

  25. Density and ideal gas

  26. What is the fault in the logic? • I noticed my tires were a bit low and went to the gas station. As I was filling the tires, I thought about the kinetic molecular theory (KMT). I realized that I was increasing both the pressure and volume of the tires. “Hmmm,” I thought, “that goes against what I learned in chemistry, where I was told pressure and volume are inversely proportional.”

  27. Dalton’s Law of Partial Pressure

  28. Dalton’s Law of Partial Pressure • The total pressure of a system is the sum of the partial pressures of all the gases that make up the system. • Ptot = P1 + P2 + P3 + … • Where Ptot is the total pressure • P1 is the pressure of gas 1 • P2 is the pressure of gas 2 • P3 is the pressure of gas 3

  29. Example • 0.750 L of a gas is collected over water at 23.0°C with a total pressure of 99.75 kPa. What is the pressure of the dry gas? The vapor pressure of water at 23.0oC is 2.81 kPa

  30. Stay tuned for more...

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