1. Properties of a Gas Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. Properties of a Gas  Reading Assignment: Zumdahl, Chapter 5.1-5.3  This lecture introduces the interrelated dependence of moles, temperature, pressure and volume of a confined gas.  Based on assumptions of ideal gas behavior, these parameters when combined form the ideal gas equation, PV=nRT.

3. Gases Large intermolecular distances, compared to molecular size No long or short range structural order What happens when the stopcock is opened?

4. Gases Mix together in any proportions Intermolecular collisions are elastic -- energy is transferred through collisions

5. Important Physical Properties of a Gas  Temperature  Pressure  Volume  Moles

6. Temperature  Temperature is a measure of molecular motion: vibration, rotation and translation  Gases move at high velocity (> 1000 m·sec –1 )  Common units: Celsius (°C), Fahrenheit (°F)  Absolute units: Kelvin (K), Rankine (°R)

7. Temperature  Absolute units: Kelvin (K), Rankine (°R)  0.00 °C = 273.15 K = 32.00 °F = 491.67 °R  100.00 °C = 373.15 K = 212.00 °F = 671.67 °R  Isothermal - constant temperature

8. Pressure Due to molecules hitting the surface Force per unit area

9. Pressure What do you know about the pressure in a balloon?

10. Pressure Within a closed container with a flexible or moveable barrier, the external forces pushing on the surface of the container containing the gas are equal to the pressure of the trapped gas pushing out.

11. Barometer mercury vacuum What forces determine the height of the mercury in the glass tube?

12. Barometer atmospheric pressure What forces determine the height of the mercury in the glass tube?

13. Barometer 760 mm  30 in How much pressure does the atmosphere exert?  Hg = 13.6 g·cm –3 = 0.490 lb·in –3 1.03 kg·cm –2 = 14.7 lb·in –2

14. Barometer How high would a water barometer have to be?  H 2 O= 1.0 g· cm –3 33 feet

15. Pressure  Common units: lbs·in –2, atmospheres (atm), mm Hg, torr, pascals (N·m –2, Pa)  1.00 atm = 14.7 lbs·in –2 = 760 mm Hg = 760 torr = 1.013 x10 5 Pa

16. Pressure  The actual atmospheric pressure is a function of the weather (high or low pressure) and altitude. Typical Terre Haute pressure is 730-750 mm Hg.  Isobaric - constant pressure

17. Volume  Gases occupy the complete volume to which they are constrained  Liquids and solids occupy a volume corresponding to their mass and density  Isochoric - constant volume

18. Moles  A counting unit for the number of molecules being considered

19. Physical Laws of Gases  Boyle's Law  Charles' Law  Avogadro's Law  Ideal Gas Law

20. Boyle's Law  P·V = constant isothermal constant amount of gas volume pressure What does a plot of this relationship look like?

21. Charles' Law VTVT isobaric constant amount of gas volume temperature What does a plot of this relationship look like? What does the y-intercept indicate?

22. Avogadro's Law VnVn isobaric isothermal volume moles of gas What does a plot of this relationship look like?

23. Gas Laws volume pressure Boyle volume temperature Charles volume moles of gas Avogadro V  1/PV  TV  n V  nT P

24. Ideal Gas Law  P·V  n·T u PV = nRT where R = ideal gas constant = 0.08205 L·atm·mol –1 ·K –1

25. Boyle's Law u P·V = constant How will this plot change if the same number of moles of gas are at a higher temperature? isothermal constant amount of gas pressure volume

26. Common Gases Room Temperature, One Atmosphere Pressure  Monatomic: He, Ne, Ar, Kr, Xe, Rn  Polyatomic Elements: N 2, O 2, O 3, F 2, Cl 2 Compounds: CO, CO 2, NO, N 2 O, NO 2, N 2 O 4, N 2 O 5, CH 4, C 2 H 6, C 2 F 4, etc.

27. Atmospheric Composition  Dry air 78% N 2, 21% O 2, 1%Ar  Normal air N 2, O 2, Ar, 0.03% CO 2, 1.6% H 2 O