Gas Law Review

1. Gas Law Review

2. Properties of Gases • No definite shape • It fills its container • Compressible • With increases in pressure • Low Density • Molecules are far apart • Intermolecular forces are ignored • Diffusion • Molecules can randomly spread out

3. Ideal Gas • Theoretical description of gases • Disregard the volume of the molecule itself • Disregard any attractive force between molecules • Real gases stray from ideal gases at: • LOW Temperatures • HIGH Pressures

4. At STP (Standard temperature and pressure), all gases have a volume of 22.4 L. • Standard Temperature: • 0oC • 273 K • Standard Pressure: • 101.3 kPa • 1 atm • 760 torr (or mmHg)

5. Charles Law • The volume of a quantity of gas, at constant pressure, varies directly with the Kelvin temperature. • Temperature MUST be in Kelvin! (oC + 273) @ constant Pressure

6. A gas is collected at 58oC and has a volume of 225mL. What volume will it occupy at standard temperature, if pressure remains constant?

7. Since the temperature decreases, pressure must decrease! T1= 331 K V1 = 225 mL T2 = 273 K V2 = ? 186 mL = 0.186 L

8. Boyles Law • As pressure increases, volume decreases. • Temperature MUST be constant.

9. A sample of O2 gas at 0.947atm has a volume of 150mL. What would its volume be at 0.987atm if the temperature stay constant?

10. P1 = 0.947 atm V1 = 150 mL P2 = 0.987 atm V2 = ? 144mL = 0.144L

11. Gay-Lussac’s Law Volume is constant * Remember, Temperature MUST be in Kelvin

12. Combined Gas Law

13. An aerosol can has a pressure of 103 kPa at 25oC. It is thrown into a fire and its temperature increases to 928oC. What will its pressure be?

14. P1 = 103 kPa P2 = ? T1 = 25 oC + 273 = 298 K T2 = 928 oC + 273 = 1201 K P2 = 415 kPa

15. The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa. What would the volume be at STP?

16. V1 = 30.0L T1 = 313 K P1 = 153 kPa V2 = ? T2 = 273 K P2 = 101.3 kPa V2 = 39.6 L

17. Ideal Gas Law P = pressure V = volume (in Liters!) n = moles T = temperatre (in Kelvin!) R = gas constant Gas constants

18. Find Volume • What volume would be occupied by 1.00 moles of gas at 0oC at 1 atm pressure?

19. P = 1 atm V = ? n = 1 mol R = 0.082 (because pressure is in atm) T = 0oC + 273 = 273 K V = 22.4L

20. Avogadro’s Principle • Equal volumes of gases at the same temperature and pressure contain equal numbers of particles. • Molar Volume- for a gas, the volume that one mole occupies at STP • Temp = 0oC or 273K • Pressure = 1 atm or 101.3 kPa or 760 torr (mmHg) 1 mole = 22.4 Liters

21. Practice • Determine the volume of a container that holds 2.4 mol of gas at STP.

22. 54 L

23. 1 H2 + 1 Cl2 2HCl • If 100L of hydrogen gas react at STP, how many grams of hydrogen chloride can form?

24. 326 g HCl

25. Dalton’s Law of Partial Pressure • The sum of the individual gas pressures equals the overall pressure of the mixture of gases.

26. If a container has 166 torr H2, 109 torr CO2 and 176 torr of O2, what is the total pressure of the mixture? 116 torr + 109 torr + 176 torr = 401 torr

27. Our atmosphere is made of 21% O2, 78% N2 and 1% other gases. At sea level (standard pressure), what is the partial pressure of oxygen? 760 torr x 0.21 = 159 torr O2

28. Diffusion • The spontaneous spreading of particles • The rate of diffusion depends on the velocities and masses of the molecules • Effusion – the process by which a gas escapes from a small hole in a container • Lighter gases ALWAYS diffuse/effuse faster than heavier molecules

29. Grahams Law of Diffusion • The relative rates at which two gases, at the same temperature and pressure, will diffuse, vary inversely as the square root of the molecular mass of the gases. **Always consider gas 1 the lighter gas

30. Compute the relative rates of diffusion of helium and argon. • go to the periodic table for molar mass of He and Ar

31. Mass He = 4 g/mol Mass Ar = 40 g/mol So, helium diffuses 3x’s faster than argon.