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Honors Chem Chapters 10, 11, and 12
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Kinetic Molecular Theory (KMT) Molecules are constantly in motion and collide with one another and the wall of a container Particles move faster with increased temperature Gases are made of mostly empty space and just a few fast moving particles.
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Properties of Gases Low Density Expansion Compressibility Fluidity Diffusion/Effusion
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Nature of Gases Diffusion: spontaneous mixing of gases
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Nature of Gases Effusion: gas particles spontaneously pass through a small opening
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Graham’s Law of Diffusion (or Effusion) Smaller, lighter gas molecules move faster through the air than larger, heavier gas molecules. “Lighter, faster, farther”
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Graham’s Law of Diffusion (or Effusion)
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Graham’s Law: Rewritten r = rate MM= Molar Mass d = distance t = time light = lighter gas heavy = heavy gas
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Kinetic Molecular Theory (KMT) Molecules are constantly in motion and collide with one another and the wall of a container Particles move faster with increased temperature Gases are made of mostly empty space and just a few fast moving particles.
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Ideal Gas Ideal Gas: a gas that perfectly conforms to assumed gas behavior (doesn’t exist) Most gases are described using real conditions and variables
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Variables of Gases (P) Pressure (V) Volume (T) Temperature (n) Amount of gas in moles
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Pressure Measures: Force exerted by moving gas particle collisions with their container
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Pressure Units Units: 1 atm (atmosphere) of pressure is the average pressure at sea level Important Conversions: 1 atm= 760 mmHg (millimeters of Mercury) = 760 torr = 101.3 kPa (kilo Pascals) = 14.7 psi (pounds per square inch)
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Volume Measures: amount of space that a gas occupies Units: Liters (L) Important Conversions: 1 L = 1000mL
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Temperature Measures: average kinetic energy of gas particles. Units: Kelvin (K) The Celsius scale is NOT used for gases because gases can still have kinetic energy at negative and 0 o C.
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Kelvin Scale and Absolute Zero Absolute Zero = 0 Kelvin represents the temperature at which a gas has NO kinetic energy
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Converting Temperature Important Conversions: o C + 273 = K K – 273 = o C
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STP STP = Standard Temperature and Pressure Exactly 0 o C and 1 atm At STP, one mole of gas (6.02 x10 23 particles) occupies 22.4 L If a gas is not held at STP, then volume is recalculated
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Gas Variables A variable is a factor that is liable to change. Pressure, temperature, and volume of a gas are liable to change. Pressure, volume, and temperature are interdependent. When variable changes, they all do.
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The Combined Gas Law Relates pressure, temperature, volume, and moles of a gas Relates initial and final conditions Variables that do not change are constants and not included in the equation
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The Combined Gas Law Equation The left side (1) represents the initial conditions of the gas The right side (2) represents the final conditions of the gas
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Charles’ Law: Volume and Temp What changes? And How? Volume increases, temperature increases What stays the same? Pressure and moles are held constant (toss ‘em)
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Charles’ Law: Equation Remember: Temperatures must be in Kelvin
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Charles’ Law: Graph Direct Relationship: both variables increase together
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Charles Law: Simulation
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Charles’ Law: Video Demo
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Charles’ Law : Example A gas sample at 25 o C and 752 mL is heated to 50 o C, what is the new volume?
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Boyle’s Law : Pressure and Volume What changes? And How? When Pressure increases, Volume decreases What stays the same? Temperature and moles are held constant (toss ‘em)
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Boyle’s Law : Equation Remember: Pressure units on both sides of the equation must be the same P 1 V 1 = P 2 V 2
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Boyle’s Law: Graph Inverse Relationship: an increase in one variable with a simultaneous decrease in the other
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Boyle’s Law: Simulation
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Boyle’s Law: Video Clip
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Boyle’s Law Example Q: A 1.0 L sample of gas is held at standard pressure, 1.0 atm. The pressure of the gas is reset to 152 mmHg. What is the new volume of the gas?
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Gay-Lussac’s Law: Pressure and Temperature What changes? And how? As temperature of a gas increases, the pressure also increases What stays the same? Volume and moles are held constant (toss ‘em)
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Gay-Lussac’s Law: Equation Pressure units on both sides of the equation must be the same Temperature must be in Kelvin
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Gay-Lussac’s Law: Graph Direct Relationship: Both variables increase together
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Gay-Lussac’s Law: Simulation
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Gay-Lussac’s Law: Video Clip
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Gay-Lussac’s Law: Example Q: A gas has a pressure of 0.370 atm at 50.0 °C. What is the pressure at standard temperature?
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