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Chemistry SM-1232 Week 2 Lesson 2

Chemistry SM-1232 Week 2 Lesson 2. Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008. Class Today. Charles’s Law: Volume and Temperature Ideal Gas Law Combined Gas Law Avagadro’s law Dalton’s law of partial pressures of gases Molar Mass

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Chemistry SM-1232 Week 2 Lesson 2

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  1. Chemistry SM-1232Week 2 Lesson 2 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008

  2. Class Today • Charles’s Law: Volume and Temperature • Ideal Gas Law • Combined Gas Law • Avagadro’s law • Dalton’s law of partial pressures of gases • Molar Mass • Gases over water • Gas Stoich • Molar Volume • Practice Problems

  3. Charles’s Law • Volume and Temperature • Temperature in this case is measured in Kelvin. • Temp C + 273 = Temp in Kelvin

  4. Charles’s Law • Temp and Volume are directly proportional • This is a system where pressure isn’t changing • Like a hot air balloon, but not like a helium balloon because the pressure would change. • This could be like a gas spreading through a classroom, but not a gas in a closed vial.

  5. Charles’s Law • Assuming the pressure is constant and the amount of gas is constant here’s the rule: • V1/T1 = V2/T2 • Solve for V1, T1, and T2

  6. Celcius • What happens to that math if we calculate using 0C instead of 273 Kelvin?

  7. Gay-Lussac • P and T are also a direct relationship when number of atoms and volume are constant. • This is like a “pressure cooker” • The chemical apparatus is also called a bomb calimeter.

  8. Three Laws • P1V1=P2V2 Boyle • P1/T1=P2/T2 Gay Lussac • V1/T1=V2/T2 Charles • HEY! These three laws look like they could all be related to one bigger one! We call it the combined gas law.

  9. Combined Gas Law • P1V1/T1= P2V2/T2 • Solve for V2 • Solve for T1 • How many different variables would you need numbers for to actually solve this problem.

  10. Avogadro’s Law • Avogadro’s number is 6.02e23 • It’s the number of atoms in 1 mole • 1 mole of atoms turns it’s atomic mass into grams. Very handy when weighing chemicals. • He also found that the volume of gas at constant pressure and temperature becomes dependant on the number of molecules of gas.

  11. Avogadro’s Law • V1/n1=V2/n2 • Where n is the number of moles of a gas.

  12. Combining Everything • Let’s figure out what V is equal to… • V ~ 1/P • V ~ T • V ~ n • Therefore, V ~ nT/P • Throw in a constant that can account for units and we get V= RnT/P aka • PV= nRT

  13. The Ideal Gas Law • PV=nRT • This describes how ideal gasses behave. • If you know 4 variables you can always figure out the last one.

  14. Ideal Gas Constant • R is the ideal gas constant • It’s value changes when we have different units in the problem • Typically R = 0.082 L atm/ mol K • That’s right, R has 4 different units associated with it. You’ll see why in a sec.

  15. New Material: Molar Mass of a Gas • Molar Mass? • Molar means having to do with moles, typically 1 mole • Mass has to do with gram or kg • Molar mass is defined as Mass/Moles • Aka Molar mass= Mass/ 1 Mole

  16. Finding Molar Mass • Typically you’ll get a set of condintions where you have to solve for n. This will give you moles. You’ll also be told the mass of the gas. That gives you grams. The mass divided by the moles will give you the molar mass.

  17. Example • A gas sample has a mass of 1.36g. It takes up .112L at 298K under 1.06 atm of pressure. What’s the molar mass. • A. Solve for n. • B. Take mass and divide by n for molar mass. • GO!

  18. Dalton’s Law of Partial Pressure • John Dalton (my boy JD), is best known for the first system of combining atoms together and for his rules describing how atoms form molecules. He’s such a rockstar though that he also figure out how partial pressures of gasses work too. • Ptotal= P1 + P2+ P3 + P4 etc…

  19. Dalton’s Law Example • At sea level the partial pressure of Nitrogen is 0.78 atm, the partial pressure of oxygen is 0.21 atm and the partial pressure of all the other little gases is 0.01 atm. What’s the total pressure at sea level?

  20. Percent composition • The percent composition of a gas can be used to calculate the partial pressure of the gas. The partial pressure is equal to the percentage a gas makes up multiplied by the total pressure. • P1= gas%*Ptotal

  21. Percent Composition • If nitrogen makes up 83% of a gas sample at 12 atm what is the partial pressure of nitrogen? What’s the partial pressure of everything else?

  22. Gas Stoich • 2H2 + O2 -> 2H2O • If you have 5.3 moles of O2 how many moles of H2 are required? • Use the molar ratio of 2H2/1O2!!!

  23. Gas Stoich • Hydrogen and Nitrogen come together to form ammonia NH3. A chemist carefully prepares Hydrogen gas; he make 34L at 2atm, at 300K. He then uses that gas to make Ammonia. How many moles of ammonia can he make? • A. Ideal gas law to get n, moles. • B. Convert moles of H2 into Moles NH3.

  24. Molar Volume • All gases take up 22.4L/1 mole at STP. • If you fill up 63L of a gas at STP how many moles do you have? • If you have 6 moles of a gas many liters will it take up? How many mL will it fill?

  25. To Do • Study Chapter 11 for quiz on Friday • Copy your notes over • Quiz on chapter 11 on Friday 10 bonus points. • HW problems due March 16. Complete 1 HW set for 2-3 people. 15 bonus points. • HW problems listed on the syllabus.

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