1. Properties of Gases Kinetic Molecular Theory: 1.Small particles (atoms or molecules) move quickly and randomly 2.Negligible attractive forces between particles 3.Most of volume of gas is empty space 4.Average kinetic energy is proportional to temperature 5.Particles in constant motion (straight paths) –As they hit the sides of container, they exert pressure 1

2. Properties of Gases 2

3. Measuring Pressure Pressure (P) http://encarta.msn.com/media_461532488_ 761573986_1_1/mercury_barometer.html Barometer: measures atmospheric pressure

4. Atmospheric Pressure 4 4 The pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

5. 5 5 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 5 Is about 1 atmosphere at sea level. Depends on the altitude and the weather. Is lower at high altitudes where the density of air is less. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Atmospheric Pressure

6. Units of Pressure pascal –Pa –10 3 Pa = 1 kPa atmosphere – atm Millimeter of mercury – mm Hg – Torr psi, pounds per square inch (engineering)

7. Boyle’s Law The volume occupied by a gas is inversely related to its pressure. T,n = constant

8. Practice Problem 1 A sample of gas has a volume of 100.0 mL at 1.0 atm. If increase the pressure to 2.0 atm, what is the new volume of the gas (T is constant)? 8

9. Charles’s Law The volume occupied by a fixed amount of gas is directly related to its absolute Kelvin temperature. P, n = constant

10. Practice Problem 2 A sample of gas has a volume of 100.0 mL at 27 ˚C. If we heat the gas to 54 ˚C (keeping pressure constant), what is the new volume of the gas? 10

11. Gay-Lussac’s Law At constant volume, pressure is directly related to temperature V, n = constant Combined Gas Law: 2 variables change; find effect on third PV/ T = constant

12. Vapor Pressure and Boiling Point 12 Pressure of gas molecules above the surface of a liquid. At the boiling point, the vapor pressure becomes equal to the external pressure.

13. Boiling Point of Water 13 Depends on the vapor pressure. Is lower at higher altitudes. Is increased by using an autoclave to increase external pressure. TABLE 7.5 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

14. Avogadro’s Law The volume occupied by a gas is directly proportional to the amount (mol) of gas (fixed T & P) V / n = constant At fixed T & P: equal volumes of any ideal gas have… equal numbers of particles equal moles of particles

15. Gas Behavior at STP STP: –Standard Temperature & Pressure –0 ˚C (273.15 K) and 1 atm (760 torr) Standard Molar Volume = 22.4141 L or 22.4 L

16. Practice Problem What is the volume in milliliters of 0.10 g of helium gas at STP? 16

17. Ideal Gas Law Combine: –Boyle’s Law –Charles’s Law –Avogadro’s Law PV = nRT Solve at STP…

18. A tank filled with methane at 23 ˚C and 0.991 atm is fitted with a safety valve that opens if internal pressure exceeds 1.00 x 10 3 torr. When the tank is placed in boiling water at exactly 100. ˚C, will the safety valve open? Initial: n = T = P = V = Final: n = T = P = V = constant 23 ˚C = 296. 15 K 0.991 atm constant ? torr constant 100 ˚C = 373.15 K

19. A sample of gas occupies 105 ml at 0.903 atm. If temperature remains constant, what is the volume (in L) at 26.3 kPa? Initial: n = T = P = V = Final: n = T = P = V = constant 0.903 atm 105 ml 26.4 kPa ? ml constant = 0.2605 atm

20. Each gas in a mixture acts like it is the only gas present –No chemical reactions –Totally miscible (homogeneous solution) Dalton’s Law of Partial Pressures: Mixtures of Gases P total = P 1 + P 2 + P 3 + …… Example: When water vapor added to pure air…. P humid air = P dry air + P added water vapor Each gas exerts a partial pressure as if it were by itself.

21. Practice Problem A sample of hydrogen gas and water vapor has a total pressure of 750. torr. How many moles of hydrogen gas are in this sample, if the hydrogen gas has a volume of 365 mL at 22 ˚C and the pressure of the water is 21 torr? 21