1. 1 CHAPTER 11 Gases and their Properties

2. 2 Density Comparison The density of gases is much less than that of solids or liquids: compoundSolid density (g/mL) Liquid density (g/mL) Gas density (g/mL) H2OH2O0.9170.9980.000588 CCl 4 1.701.590.00503  Gas molecules are extremely far apart compared to liquids and solids

3. 3 Pressure force per unit area (N/m 2 ) Atmospheric pressure is measured using a barometer –Measures of standard pressure: 760.0 mm Hg 760.0 torr 1.000 atmosphere 101.3 kPa (1 Pa = 1 N/m 2 ) Hg density = 13.6 g/mL

4. 4 Boyle’s Law Relates the compressibility of gases to pressure and volume at constant temperature For a gas: –P  1/V at constant temperature and # of moles of gas –P 1 V 1 = c 1 for gas at one pressure and volume –P 2 V 2 = c 2 for gas at a 2 nd pressure and volume –c 1 = c 2 for the same gas at the same T Boyle’s Law: P 1 V 1 = P 2 V 2 (constant mole of gas and constant temperature) Note: temperature should be measured in Kelvin

5. 5 Boyle’s Law: Example: At 25 o C a sample of He has a volume of 4.00 x 10 2 mL under a pressure of 7.60 x 10 2 torr. What volume would it occupy under a pressure of 2.00 atm at the same temperature?

6. 6 Charles’ Law Relates the compressibility of gases to temperature and volume at constant pressure Note: temperature should be measured in Kelvin

7. 7 Charles’ Law: Example: A sample of hydrogen, H 2, occupies 1.00 x 10 2 mL at 25.0 o C and 1.00 atm. What volume would it occupy at 50.0 o C under the same pressure?

8. 8 Standard Temperature and Pressure (STP) It is a reference point for gas calculations –Standard Pressure: – 1.00000 atm or 101.3 kPa –Standard Temperature: 273.15 K or 0.00 o C

9. 9 The Combined Gas Law Note: temperature should be measured in Kelvin Boyle’s LawCharles’ Law Combined Gas Law

10. 10 The Combined Gas Law Equation Example: A sample of nitrogen gas, N 2, occupies 7.50 x 10 2 mL at 75.0 0 C under a pressure of 8.10 x 10 2 torr. What volume would it occupy at STP?

11. 11 Avogadro’s Law two gases at the same temperature and pressure with equal volumes, contain the same number of molecules (or moles) of gas If you set temperature & pressure for any gas to STP: –-one mole of that gas has a volume 22.414 L standard molar volume –-this is the standard molar volume –-V  moles (n) Example: 11.2 L of a gas at STP is how many moles? Example: 44.8 L of a gas at STP = ? moles

12. 12 Avogadro’s Law Example: 1.00 mole of a gas occupies 36.5L and its density is 1.36 g/L at some unspecified temperature and pressure (a) What is its molar mass? (b) What is its density at STP?

13. 13 The Ideal Gas Law –Example: 1.0000 mole of a gas at STP (1.0000 atm, and 273.15 K), has a volume of 22.414 L. Find R- the gas constant. PV = nRT

14. 14 The Ideal Gas Law Example: What volume would 50.0 g of ethane, C 2 H 6, occupy at 1.40 x 10 2 o C under a pressure of 1.82 x 10 3 torr? PV = nRT

15. 15 Dalton’s Law of Partial Pressures The pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases P total = P A + P B + P C +.....

16. 16 Dalton’s Law of Partial Pressures Example: If 1.00 x 10 2 mL of hydrogen, measured at 25.0 o C and 3.00 atm pressure, and 1.00 x 10 2 mL of oxygen, measured at 25.0 o C and 2.00 atm pressure. The hydrogen gas was forced into the container of oxygen gas at 25.0 o C. What would be the pressure of the mixture of gases?

17. 17 Gas Laws and Chemical Reactions 2 mol KClO 3 2 mol KCl 3 mol O 2 or 2(122.5g/mol) 2 (74.6g/mol)3(32.0g/mol) 3 moles of O 2 can also be thought of as: 3(22.4L) or67.2 L at STP

18. 18 Example: What volume of oxygen measured at STP, that can be produced by the thermal decomposition of 120.0 g of KClO 3 ? 122.5g/mol 74.6g/mol 32.0g/mol Gas Laws and Chemical Reactions

19. 19 Diffusion and Effusion of Gases Diffusion: the intermingling (mixing) of gases Effusion: the escape of gases through tiny holes