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Gas Laws

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Learning Objectives TLW know the variables that influence the behavior of gases (TEKS 9) TLW be able to describe interrelationships between temperature, number of moles, pressure, and volume of gases in an enclosed system (TEKS 9.A) TLW perform stoichiometric calculations to determine mass and volume relationships between reactants and products involving gases (TEKS 9.B) TLW describe the postulates of kinetic molecular theory (TEKS 9.C)

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I. Gas Laws A. Four properties of gases 1. Volume - V –gases do not have a defined volume –particles of a gas expand to fill their container –volume is measured in L (liters) 2. Pressure – P –collisions of particles with a surface –P measured in atm, kPa, torr, mm Hg

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3. Temperature – T o –the measure of average particle speed –gas particles are in constant motion –T o for gases are measured in K (Kelvin) 4. Quantity – n –measure of how much there is of a gas –MOLES!!!!! – 22.4 L of gas = 1 mole

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Postulates of Kinetic Molecular Theory Gases are composed of a large number of particles that behave like hard, spherical objects in a state of constant, random motion. These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space. There is no force of attraction between gas particles or between the particles and the walls of the container. These particles move in a straight line until they collide with another particle or the walls of the container. Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container. The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.

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Postulates of Kinetic Molecular Theory Check out this interactive tool which demonstrates the postulates in action eculartheory/basicconcepts.html

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B. Gas laws are based mathematically on the relationship of the four properties of gas volume pressure temperature quantity

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II. The Gas Laws (4 major ones) A. Boyles Law 1. Discovered that gas pressure and volume are related 2. If pressure is increased then volume decreases 3. Pressure and volume are inversely related 4. Meaning = whatever pressure does volume does the opposite

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NASA Video

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Boyles Law V P P 1 V 1 = P 2 V 2

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5. Example of Boyles Law A sample of gas has a volume of 4.2 L and a pressure of 0.95 atm. If the pressure on the balloon increases to 1.90 atm what will the new volume be? 0.95 atm 4.2 L 1.90 atm V = ? P 1 V 1 = P 2 V 2 (.95 atm)(4.2L) = (1.90 atm)V 2 V 2 = 2.1 L

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B. Charles Law 1. Discovered the relationship between volume and temperature 2. If T o increases then the volume increases 3. T o and volume are directly proportional 4. Meaning = whatever volume does T o does the exact same thing

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NASA Video

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Charles Law T V V 1 /T 1 = V 2 /T 2 NOTE: All T o must be Kelvin!!!! o C = K

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5. Example of Charles Law Another sample of gas has a volume of 2.0 L and a T o of 100 o C. If the T o is increased to 200 o C, what will the new volume be? V = 2.0L 100ºC V = ? 200ºC V 1 /T 1 = V 2 /T 2 2.0L/(100 o C + 273) = V 2 /(200 o C + 273) V 2 = 2.54 L KELVIN!!!!!!!!

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C. Gay-Lussacs Law 1. Discovered the relationship between Pressure and T o 2. If T o increases then Pressure increases 3. T o and P are directly proportional 4. Meaning = whatever T o does pressure does the exact same thing

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Gay-Lussacs Law P 1 /T 1 = P 2 /T 2 T P

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Example of Gay-Lussacs Law Another sample of gas has a volume of 2.0 L a T o of 25 o C, and a pressure of 2.00 atm. If the T o is increased to 75 o C, what will the new pressure be? 25ºC 2.00 atm V = 2.0L 75ºC V = 2.0L P = ? P 1 /T 1 = P 2 /T atm/(25 o C + 273) = P 2 /(75 o C + 273) P 2 = 2.34 atm

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D. Avogadros Law If pressure and temperature are kept constant, the volume of a gas is directly proportional to number of moles of a gas This is why a balloon gets larger as you blow it up… not the pressure 1 mole of gas = 22.4 L Mathematically speaking….. V 1 = V 2 n 1 n 2

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Example of Avogadros Law I have a balloon with 0.25 moles of air in it and its volume is 0.30 L. If I blow it up more to 0.75 L, how many moles have I added of air? V 1 /n 1 = V 2 /n L =0.75 L = 0.63 moles 0.25 molesn 2 moles

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E. Combined Gas Law 1. Sometimes the pressure, temperature, and/or change 2. So must combine formulas from all three dudes. 3. Looks like this P 1 V 1 = P 2 V 2 T 1 T 2

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Example of combined gas law 8.0L of neon gas at 23 o C and 900 mm Hg is then compressed to 2.0 L and the T o is raised to 225 o C. What will the new P be? P 1 V 1 /T 1 = P 2 V 2 /T 2 (900 mm Hg)(8.0 L)/(23 ºC + 273) = P 2 (2.0 L)/(225 ºC + 273) P 2 = 6057 mm Hg

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F. Ideal Gas Law PV = nRT Where R = L atm/mol °K

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Web Exploration ASPIRE Animation Activity (link)link Gas Law Investigation (link)link –Data Collection Sheet (link)link

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More Practice on Following Slides

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Sample problem #1 We will use Boyles Law: P 1 V 1 = P 2 V 2 (500.mm)(400.mL)=(250.mm)(V 2 ) V 2 = (500)(400) = 800. mL 250 A gas occupies a volume of 400. mL at 500. mm Hg pressure. What will be its volume, at constant temperature, if the pressure is changed to 250 torr? (1 mm Hg = 1 torr)

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GIVEN: V 1 = 473 cm 3 T 1 = 36°C = 309K V 2 = ? T 2 = 94°C = 367K WORK: V 1 /T 1 = V 2 /T 2 Sample #2 A gas occupies 473 cm 3 at 36 °C. Find its volume at 94 °C. CHARLES LAW T V (473 cm 3 )/(309 K)=V2/(367K) V 2 = (V 1 T 2 )/T 1 V 2 = 562 cm 3

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GIVEN: P 1 = 765 torr T 1 = 23°C = 296K P 2 = 560. torr T 2 = ? WORK: P 1 /T 1 = P 2 /T 2 Sample #3 A gas pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? GAY-LUSSACS LAW P T 765 torr/296K = 560torr/T 2 T 2 = (P 2 T 1 )/P 1 T 2 = 217 K

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Sample problem #4 A gas occupies a volume of 410 mL at 27°C and 740 mm Hg pressure. Calculate the volume the gas would occupy at STP. (0 o C & 760 mm Hg) We will use the combined gas law: Oops…use Kelvin 27°C=300K; 0°C=273K

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Independent Practice Calculations using four Gas Law Formulas Remember: o K = o C STP (Standard Temperature and Pressure) is 0 o C and 760 mm Hg = 1 atm = kPa = 14.7 psi. 1 torr = 1 mm Hg 22.4 L = 1 mole of gas R = L atm/mol °K

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Daltons Law of Partial Pressure Sum of the pressures of each gas equals total pressure of system P 1 + P 2 + P 3 + …. + P n = P total A gas is 48% O 2 & 52% N 2. Total pressure is 100 kPa. What is the pressure of each gas? 100(.48) = 48 kPa for O 2 and 100(.52) = 52 kPa for N 2

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Lab Gas Law Smorgasbord (link)link In Periodic Groups, read the entire procedure Determine potential hazards, precautions to take, PPE that might be needed

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