The Nature of Gases

1. The Nature of Gases • Gas Pressure –the force exerted by a gas per unit surface area of an object • Due to: a) force of collisions b) number of collisions

2. The Nature of Gases • The SI unit of pressure is the pascal (Pa) • Other units: • millimeters of mercury (mm Hg) • torr (torr) • atmospheres (atm)

3. The Nature of Gases • Conversions between pressure… 1 atm = 760 mmHg = 760 torr = 101,325 Pa • Convert the following measurement into mmHg, 596 torr. • Convert your answer for number 1 into atm.

4. Temperature Conversions • Temperature is measured in… • Kelvin • Conversion Factor: • C = K – 273 • K = C + 273

5. The Nature of Gases • Standards!! • temperature of 0oC (273K) • pressure of 1 atm • This is called Standard Temperature and Pressure, or STP

6. The Gas Laws are mathematical • The gas laws will describe HOW gases behave.

7. Boyle’s Law Relates Pressure and Volume they are inversely related at constant temperature. P1 V1 = P2 V2 T = constant

8. Boyle’s Law When the volume goes up, the pressure goes down V P (at constant T)

9. Charles’ Law • The volume is directly to the temperature, with constant pressure.

10. Charles’ Law • As one goes up so does the other.

11. Gay-Lussac’s Law • At constant volume, pressure and temperature are directly related. V = constant

12. Gay-Lussac’s Law As one goes up so does the other.

13. The Combined Gas Law The combined gas law is between pressure, volume and temperature.

14. If the temperature remains constant... x P1 P2 V1 x V2 = T1 T2 Boyle’s Law

15. If the pressure remains constant... P1 V1 P2 x V2 x = T1 T2 Charles’s Law

16. If the volume remains constant... P1 V1 P2 x V2 x = T2 T1 Gay-Lussac’s Law

17. Lab Describe what is happening What variables are being observed? Which Gas Law/s does it represent?

18. Gas Law Problems • Create 3 Gas Law problems • Give the proper information needed to solve • Do not tell which Gas Law it is. Create an answer key telling which Gas Law it is and how to solve. • Switch problems with a partner and solve each problem; tell what law each problem is and how to solve it. • Once you have solved all problems switch back and check each others answers.

19. Ideal Gas Law &Dalton’s Law of Partial Pressure

20. Ideal Gas Law PV = nRT R is the ideal gas constant. R = 0.0821 L atm/ mol K Tells you about a gas NOW. The other laws tell you about a gas WHEN IT CHANGES.

21. Ideal Gas Law Using this equation (PV = nRT) we can rearrange it to solve for P, V, n and T. Try to rearrange the equation to solve for P, V, n and T. • Did you get… P = nRT / V V = nRT / P n = PV / RT T = PV / nR

22. Dalton’s Law of Partial Pressures States that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases. PTotal = P1 + P2 + P3 + . . .

23. Dalton’s Law of Partial Pressures • Example: A mixture of oxygen gas, carbon dioxide gas, and nitrogen gas has a total pressure of 0.97 atm. What is the partial pressure of oxygen gas, if the partial pressure of carbon dioxide if 0.70 atm and nitrogen is 0.12 atm?

24. DLPP-PP 1.Find the total pressure of a mixture that contains three gases with the following partial pressures: 6.6 kPa, 3.2 kPa, and 1.2 kPa. 2. Find the total pressure of a mixture that contains five gases with the following partial pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa, 12.50 kPa, and 2500 Pa. 3. Find the partial pressure of ammonia in a mixture of three gases with a total pressure of 75.6 kPa if the sum of the partial pressures of the other two gases is 34.9 kPa.

25. Practice Problems A cylinder of argon gas contains 50.0 L of Ar at 18.4 atm and 127 °C. How many moles of argon are in the cylinder? A 283.3-g sample of X2(g) has a volume of 30 L at 3.2 atm and 27 °C. What is element X?

26. Practice Problems An ideal gas sample is confined to 3.0 L and kept at 27 °C. If the temperature is raised to 77 °C and the initial pressure was 1500 mmHg, what is the final pressure?

27. Practice Problems A sample of helium was compressed at 35 °C from a volume of 0.5 L to 0.25 L where the pressure is 500 mmHg. What was the original pressure?

28. Practice Problems A hot air balloonist puts 125,000 Liters of air into their balloon at 27 °C and atmospheric pressure. When they heat the air to 200 °C at constant pressure, what is the final volume of the air in the balloon?

29. Get with your lab partners Using paper, glue, etc… demonstrate the Gas Law assigned to your group. You may construct something, draw something, or create a poster. Your project must include an experiment in which you test your Gas Law properties. You have 45 minutes before you have to present your ideas to the class.

30. The Nature of Gases • Kinetic refers to motion • The kinetic-molecular theory describes the behavior of gases in terms of particles in motion!

31. The Nature of Gases • Three basic assumptions of the kinetic theory as it applies to gases: #1. Particle Size: Gases are composed of particles- • Small, hard spheres • Insignificant volume; relatively far apart from each other • No attraction or repulsion between particles

32. The Nature of Gases #2. Particle Motion: Particles in a gas move rapidly in constant random motion • Move in straight paths, changing direction only when colliding with one another or other objects

33. The Nature of Gases #3. Particle Energy: Collisions are perfectly elastic- meaning… • kinetic energy is transferred without loss

34. Phase Diagrams

35. Phase Changes 13.4 • Prepare a Poster on Phase Changes • Include all important information for each portion *See handout • You may explain your information as your group sees fit. • After 30 min you will present to the class