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I. Physical Properties

Ch. 11 - Gases. I. Physical Properties. A. Kinetic Molecular Theory. Particles in an ideal gas… have no volume. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature.

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I. Physical Properties

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  1. Ch. 11 - Gases I. Physical Properties

  2. A. Kinetic Molecular Theory • Particles in an ideal gas… • have no volume. • have elastic collisions. • are in constant, random, straight-line motion. • don’t attract or repel each other. • have an avg. KE directly related to Kelvin temperature.

  3. B. Real Gases • Particles in a REAL gas… • have their own volume • attract each other • Gas behavior is most ideal… • at low pressures • at high temperatures • in nonpolar atoms/molecules

  4. C. Characteristics of Gases • Gases expand to fill any container. • random motion, no attraction • Gases are fluids (like liquids). • no attraction • Gases have very low densities. • no volume = lots of empty space

  5. C. Characteristics of Gases • Gases can be compressed. • no volume = lots of empty space • Gases undergo diffusion & effusion. • random motion

  6. D. Temperature K = ºC + 273 ºF -459 32 212 ºC -273 0 100 K 0 273 373 • Always use absolute temperature (Kelvin) when working with gases.

  7. E. Pressure Which shoes create the most pressure?

  8. E. Pressure Aneroid Barometer Mercury Barometer • Barometer • measures atmospheric pressure

  9. E. Pressure U-tube Manometer Bourdon-tube gauge • Manometer • measures contained gas pressure

  10. E. Pressure • KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

  11. F. STP Standard Temperature & Pressure 0°C273 K 1 atm101.325 kPa -OR- STP

  12. V T P Ch. 11 - Gases II. The Gas Laws

  13. A. Boyle’s Law P V • The pressure and volume of a gas are inversely related • at constant mass & temp PV = k

  14. A. Boyle’s Law

  15. B. Charles’ Law V T • The volume and absolute temperature (K) of a gas are directly related • at constant mass & pressure

  16. B. Charles’ Law

  17. C. Gay-Lussac’s Law P T • The pressure and absolute temperature (K) of a gas are directly related • at constant mass & volume

  18. D. Combined Gas Law P1V1 T1 P2V2 T2 = P T V T PV T PV = k P1V1T2 =P2V2T1

  19. E. Gas Law Problems • A gas occupies 473 cm3 at 36°C. Find its volume at 94°C. CHARLES’ LAW GIVEN: V1 = 473 cm3 T1 = 36°C = 309K V2 = ? T2 = 94°C = 367K T V WORK: P1V1T2 = P2V2T1 (473 cm3)(367 K)=V2(309 K) V2 = 562 cm3

  20. E. Gas Law Problems • A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. BOYLE’S LAW GIVEN: V1 = 100. mL P1 = 150. kPa V2 = ? P2 = 200. kPa P V WORK: P1V1T2 = P2V2T1 (150.kPa)(100.mL)=(200.kPa)V2 V2 = 75.0 mL

  21. E. Gas Law Problems • A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP. COMBINED GAS LAW P T V GIVEN: V1=7.84 cm3 P1=71.8 kPa T1=25°C = 298 K V2=? P2=101.325 kPa T2=273 K WORK: P1V1T2 = P2V2T1 (71.8 kPa)(7.84 cm3)(273 K) =(101.325 kPa)V2 (298 K) V2 = 5.09 cm3

  22. E. Gas Law Problems • A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? GAY-LUSSAC’S LAW GIVEN: P1 = 765 torr T1 = 23°C = 296K P2 = 560. torr T2 = ? P T WORK: P1V1T2 = P2V2T1 (765 torr)T2 = (560. torr)(296K) T2 = 217 K

  23. END OF QUIZ I MATERIAL

  24. Ch. 11 - Gases III. Ideal Gas Law

  25. A. Avogadro’s Principle V n • Equal volumes of gases contain equal numbers of moles • at constant temp & pressure • true for any gas

  26. A. Ideal Gas Law p. 384 = k V n Merge the Combined Gas Law with Avogadro’s Principle: PV T PV nT = R UNIVERSALAS CONSTANT R=0.0821 Latm/molK R = 62.4 Lmm Hg/molK (torr) R=8.315 dm3kPa/molK You don’t need to memorize these values!

  27. A. Ideal Gas Law PV=nRT UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R = 62.4 Lmm Hg/molK (torr) R=8.315 dm3kPa/molK You don’t need to memorize these values!

  28. C. Ideal Gas Law Problems • Calculate the pressure in atmospheres of 0.412 mol of He at 16°C & occupying 3.25 L. GIVEN: P = ? atm n = 0.412 mol T = 16°C = 289 K V = 3.25 L R = 0.0821Latm/molK WORK: PV = nRT P(3.25)=(0.412)(0.0821)(289) L mol Latm/molK K P = 3.01 atm

  29. C. Ideal Gas Law Problems WORK: 85 g 1 mol = 2.7 mol 32.00 g • Find the volume of 85 g of O2 at 25°C and 104.5 kPa. GIVEN: V=? m=85 g T=25°C = 298 K P=104.5 kPa R=8.315dm3kPa/molK n= 2.7 mol PV = nRT (104.5)V=(2.7) (8.315) (298) kPa mol dm3kPa/molKK V = 64 dm3

  30. Let’s Practice!! Handout p.24 Things to remember: • OMIT 5 & 6 • Convert temperatures to Kelvin (add 273) • Convert all volumes to Liters (mL to L  divide by 1000) • Use R value that matches pressure unit

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