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Bell Ringer

P 1. V 1. P 2. V 2. T 1. T 2. =. Bell Ringer. 298 K. A sample of nitrogen occupies 10.0 liters at 25ºC and 98.7 kPa. What would be the volume at 20ºC and 102.7 kPa? A 7.87 L B 9.45 L C 10.2 L D 10.6 L.

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Bell Ringer

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  1. P1 V1 P2 V2 T1 T2 = Bell Ringer 298 K A sample of nitrogen occupies 10.0 liters at 25ºC and 98.7 kPa. What would be the volume at 20ºC and 102.7 kPa? A 7.87 L B 9.45 L C 10.2 L D 10.6 L A sample of nitrogen occupies 10.0 liters at 25ºC and 98.7 kPa. What would be the volume at 20ºC and 102.7 kPa? A 7.87 L B 9.45 L C 10.2 L D 10.6 L 293 K T2 T2 P2 P2 P1 V1 T2 V2 = T1 P2 (98.7 kPa) (10.0 L) (293 K) V2 = (298 K) (102.7 kPa)

  2. Gas Laws Quiz Good Luck!!

  3. For Next Class: • Homework: • Gas Laws Packet #2, problems 1-10 • Quiz next class on Ideal Gas Law, Partial Pressures, and Density • 5 questions; 22 points total • 2 short answer/FITB (2 points each) • 3 math problems (6 points each)

  4. The Ideal Gas Law & Co. Ms. Besal 3/14/2006

  5. We that we live in an world where: Gas particles have no mass Gas particles have no volume Gas particles have elastic collisions A Reminder… assume ideal These assumptions are used when trying to calculate the AMOUNT of a gas we have!

  6. Why are these assumptions important? PV = nRT Image source: thefreedictionary.com

  7. P V n R T PV = nRT The Ideal Gas Law RESSURE OLUME MOLES OF GAS GAS CONSTANT EMPERATURE Image source: popartuk.com

  8. 8.31 kPa · L 0.0821 atm · L mol · K mol · K 62.4 mmHg · L mol · K The MysteRious R • R is a constant (doesn’t change). • Number value of R depends on other units. • Units of R are a combination of many units. Image source: toysrusemail.com

  9. Ummm… What? PV = nRT Solve for R: P V R = n T Plug in units: (mm Hg) (L) (kPa) (atm) R = (mol) (K)

  10. V1 V2 = T1 T2 P1 V1 P2 V2 = T1 T2 Gas Laws, Gas Laws Everywhere! Charles' Law Boyle's Law P1 x V1 = P2 x V2 Combined Gas Law Ideal Gas Law Used with CHANGING CONDITIONS P V = n R T Used with only ONE SET OF CONDITIONS

  11. When to Use PV = nRT • Calculating amount of gas in moles • Calculating P, V, or T if moles of gas are known. • IMPORTANT! We must have 3 out of 4 pieces of information: • P • V • n • T

  12. 0.0821 L · atm mol · K Practice with the Ideal Gas Law • A gas sample occupies 2.62 L at 285ºC and 3.42 atm. How many moles are present in this sample? PV = nRT P V n = R T (3.42 atm) (2.62 L) n = = 0.196 mol (558 K)

  13. But Let’s Be Practical… We don’t usually measure in moles! We usually measure quantities in GRAMS! PV = nRT PVM = gRT

  14. P V M g R T PVM = gRT RESSURE OLUME OLAR MASS OF GAS (g/mol) RAMS OF GAS GAS CONSTANT EMPERATURE Image source: popartuk.com

  15. 4.00 g mol 0.0821 L · atm mol · K Practice with the Ideal Gas Law A balloon is filled with 0.2494 g of helium to a pressure of 1.26 atm. If the desired volume of the balloon is 1.250 L, what must the temperature be in ºC? P V M PVM = gRT T = g R (1.26 atm) (1.250 L) T = 308 K = - 273 (0.2494 g) 35 ºC

  16. PV=nRT vs. PVM=gRT • Use PV=nRT when: • You are given moles in the problem. • You are searching for moles as an answer. • Use PVM=gRT when: • You are given grams in the problem. • You are searching for grams as an answer.

  17. What Else Happens Under Unchanging Conditions? At constant V and T, pressure is easy to calculate! “The sum of the individual pressures is equal to the total pressure.” Total Pressure = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 + Pressure of gas 4 … Ptotal = P1 + P2 + P3 + … Dalton's Law of Partial Pressures

  18. Partial Pressures Practice A sample of hydrogen gas is collected over water at 25ºC. The vapor pressure of water at 25ºC is 23.8 mmHg. If the total pressure is 523.8 mmHg, what is the partial pressure of the hydrogen? Ptotal = PH2 + PH2O = 523.8 mm Hg PH2 + 23.8 mm Hg = PH2 500.0 mm Hg Source: 2003 EOC Chemistry Exam

  19. D M = V What do Changing Conditions Affect? We have learned that we can change 3 variables: Temperature, Volume, and Pressure. If MASS remains constant… …But VOLUME changes… Then DENSITY CHANGES!

  20. P1 V1 P2 V2 = T1 T2 Two Types of Density Problems: At STP: Not at STP: • molar volume of any gas at STP = • Determine new volume (V2 ) using Combined Gas Law 22.4 Liters STP Values non-STP • Density at STP = • Density at non-STP = molar mass molar mass molar volume 22.4 Liters V2

  21. D = molar mass V2 P1 = 1.0 atm V1 = 22.4 L T1 = 273 K P2 = 3.0 atm V2 = ? T2 = 314 K D = 30.08 g P1 V1 P2 V2 = 8.6 L T1 T2 Practice with Density Problems: Determine the density of ethane (C2H6) at STP: Determine the density of C2H6 at 3.0 atm and 41ºC. V2 = 8.6 L molar mass D (at STP) = molar volume V2 = P1 V1 T2 molar mass = 30.08 g T1 P2 molar volume = 22.4 L V2 = (1.0 atm) (22.4 L) (314 K) = 3.5 g/L (273 K) (3.0 atm) 30.08 g D = = 1.34 g/L 22.4 L V2 = 8.6 L

  22. For Next Class: • Homework: • Gas Laws Packet #2, problems 1-10 • Quiz next class on Ideal Gas Law, Partial Pressures, and Density • 5 questions; 22 points total • 2 short answer/FITB (2 points each) • 3 math problems (6 points each)

  23. What do Changing Conditions Affect? • Density • Stoichiometry problems So Far: Now… STP Non-STP

  24. Mass-Volume at Non-STP Two parts to solving these problems: • Use Stoichiometry • Use Gas Law

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