Gas Laws

1. Gas Laws Chemistry is “Real” gas

2. Pressure • Pressure is force per unit area • Standard atmospheric pressure • 1 atmosphere • 760 mm Hg = 760 torr • 29.92 inches Hg • 101.325 kPa • 14.7 psi

3. Barometers Mercury barometer

4. Manometers Open arm manometer

5. Manometers Open arm manometer

6. Manometers Closed arm manometer

7. Pressure • Converting units • Convert 728 torr into atmospheres. • 728 torr x 1 atmosphere 760 torr = 0.958 atm • Convert 86 kPa into torr. • 86 kPa x 760 torr 101.325 kPa = 645 torr

8. Pressure and volume: Boyle’s Law • As pressure is increased, volume decreases by the same fraction (constant temperature) P1V1 = P2V2 • Find the new volume if the gas in a 4.5 mL syringe is compressed from 1.05 atm to 2.31 atm.

9. Boyle’s Law • Make a list of variables • P1 = 1.05 atm V1 = 4.5 mL • P2 = 2.31 atm V2 = V2 • Plug variables into equation and solve for V2 1.05 atm x 4.5 mL = 2.31 atm x V2 2.31 atm 2.31 atm 1.05 x 4.5 mL = V2 2.31 = 2.05 mL

10. Boyle’s Law • Freddie Krueger compresses air in a syringe from 5.1 mL to 1.9 mL. If the gas was initially at 101 kPa, what is the new pressure? 101 kPa x 5.1 mL = P2 x 1.9 mL 101 x 5.1kPa = P2 1.9 = 271 kPa

11. Boyle’s Law • Kinetic explanation of Boyle’s Law – when volume is decreased, particles of a gas have less room and strike the walls of the container more often.

12. Temperature and volume: Charles’ Law • As the temperature increases, the volume increases (constant pressure) • V1/T1 = V2/T2 • (T must be in kelvins) • George of the Jungle has a syringe of nitrogen gas with volume 4.9 mL. The temperature of the jungle is 40ºC (313K). He places the syringe in a pot of boiling water (100ºC, 373K). What is the new volume?

13. Charles’ Law • List variables: V1 = 4.9mL T1 = 313K V2 = V2 T2 = 373K • Plug variables into Charles’ Law equation and solve for V2 4.9mL V2 313K 373K =

14. Charles’ Law • Solve for V2 4.9mL V2 313K 373K 4.9mLx373K = V2 313K = 5.84 mL =

15. Charles’ Law • Jim Jones has a syringe full of hydrogen cyanide gas (9.4 mL) at 33ºC. He submerges it in dry ice/carbon tetrachloride and the volume goes down to 7.6 mL. What is the temperature of the dry ice/carbon tetrachloride?

16. Charles’ Law V1/T1 = V2/T2 9.4 mL 7.6 mL 306K T2 9.4 1 (306Kx7.6) T2 (306Kx7.6)/9.4 = T2 = 247K (-26ºC) = =

17. Charles’ Law • Kinetic explanation of Charles’ Law – as temperature increases, the particles move faster and hit the walls of the container harder, increasing the volume. • In a rigid container the pressure increases. (Gay-Lussac’s Law)

18. Combined Gas law • Combination of Boyle’s and Charles’ Laws P1V1 = P2V2 T1 T2 • The amount of gas remains constant.

19. Combined Gas Law • Jane compresses a sample of fluorine gas at standard pressure in a syringe from 6.2 mL to 2.3 mL. As she does this the temperature of the gas increases from 296K to 310K. What is the new pressure of the gas in atmospheres?

20. Combined Gas Law 1atm x 6.2 mLP2 x 2.3 mL 296K 310K 1 x 6.2 x 310 P2 296 x 2.3 = 2.8 atm = =

21. Combined Gas Law • JJ leaves his basketball on the hot pavement on a summer afternoon. The pressure in the ball increases from 20.7 psi to 21.3 psi. The internal temperature of the ball went from 22ºC to 41ºC. If the original volume was 5.2 liters, what is the final volume?

22. Combined Gas Law P1V1 = P2V2 T1 T2 20.7psi x 5.2 L = 21.3psi x V2 295K 314K 20.7psi x 5.2 L x 314K = V2 295K x 21.3psi = 5.4 L

23. Law of combining gas volumes • Under the same conditions, equal volumes of any gas contain the same number of particles (Avogadro’s principle) • Standard conditions – 0ºC (273K) and 1 atm • Under standard conditions, one mole of a gas occupies 22.4 liters (molar volume)

24. Law of combining gas volumes • In a reaction where all the reactants and products are gases, the mole ratios are also volume ratios • 2H2 + O2 2H2O