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Chapter 12 Gases

Chapter 12 Gases. Pressure and Volume (Boyle’s Law) Temperature and Volume (Charles’ Law) Temperature and Pressure (Gay-Lussac’s Law). Boyle's Law. The pressure of a gas is inversely related to the volume (T constant). P increases and V decreases. P 1. P 2. V 1. V 2.

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Chapter 12 Gases

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  1. Chapter 12Gases Pressure and Volume (Boyle’s Law) Temperature and Volume (Charles’ Law) Temperature and Pressure (Gay-Lussac’s Law) Lecture PLUS Timberlake 2000

  2. Boyle's Law The pressure of a gas is inversely related to the volume (T constant). Lecture PLUS Timberlake 2000

  3. P increases and V decreases P1 P2 V1 V2 Lecture PLUS Timberlake 2000

  4. Pressure and Volume Experiment Pressure Volume P x V (atm) (L) (atm x L) 1 8.0 2.0 16 2 4.0 4.0 _____ 3 2.0 8.0 _____ 4 1.0 16 _____ Boyle's Law P x V = k (constant) when T remains constant P1V1= 8.0 atm x 2.0 L = 16 atm L P2V2= 4.0 atm x 4.0 L = 16 atm L P1V1 = P2V2 = k Use this equation to calculate how a volume changes when pressure changes, or how pressure changes when volume changes. new vol. old vol. x Pfactor new P old P x Vfactor V2 = V1 x P1 P2 = P1 x V1 P2 V2 Lecture PLUS Timberlake 2000

  5. Boyle's Law The product P x V remains constant. P1V1 = P2V2 P1V1= 8.0 atm x 2.0 L = 16 atm L P2V2= 2.0 atm x 8.0 L = 16 atm L Lecture PLUS Timberlake 2000

  6. PV Problem Freon-12, CCl2F2, is used in refrigeration systems. What is the new volume (L) of a 1.6 L sample of Freon gas initially at 50 mm Hg after its pressure is changed to 200 mm Hg at constant T? Lecture PLUS Timberlake 2000

  7. PV Calculation Prepare a data table DATA TABLE Initial conditions Final conditions P1 = 50 mm Hg P2 = 200 mm Hg V1 = 1.6 L V2 = ? Lecture PLUS Timberlake 2000

  8. Find New Volume (V2) When pressure increases, volume must decrease. Multiply the initial volume by a pressure ratio with the smaller pressure on top. V2 = 1.6 L x 50 mm Hg = 0.4 L 200 mm Hg Lecture PLUS Timberlake 2000

  9. New Volume (V2)Using PV Equation Solve for V2: P1V1 = P2V2 V2 = P1V1 P2 V2 = 1.6 L x 50 mm Hg = 0.4 L 200 mm Hg Lecture PLUS Timberlake 2000

  10. Learning Check GL1 A sample of nitrogen gas is 6.4 L at a pressure of 0.70 atm. What is the new volume when the pressure is 1.40 atm (T constant)? 1) 3.2 L 2) 6.4 L 3) 12.8 L Lecture PLUS Timberlake 2000

  11. Solution GL1 6.4 L x 0.70 atm = 3.2 L (1) 1.40 atm Volume must decrease to cause an increase in the pressure Lecture PLUS Timberlake 2000

  12. Learning Check GL2 A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain. 1) 200. mm Hg 2) 400. mm Hg 3) 1200 mm Hg Lecture PLUS Timberlake 2000

  13. Solution GL2 A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain. 600. mm Hg x 12.0 L = 200. mm Hg (1) 36.0 L Pressure decreases when volume increases. Lecture PLUS Timberlake 2000

  14. Charles’ Law V = 125 mL V = 250 mL T = 273 K T = 546 K Observe the V and T of the balloons. How does volume change with temperature? Lecture PLUS Timberlake 2000

  15. Charles’ Law: V and T At constant pressure, the volume of a gas is directly related to its absolute (K) temperature V1 = V2 T1 T2 Lecture PLUS Timberlake 2000

  16. Learning Check GL3 Use Charles’ Law to complete the statements below: 1. If final T is higher than initial T, final V is (greater, or less) than the initial V. 2. If final V is less than initial V, final T is (higher, or lower) than the initial T. Lecture PLUS Timberlake 2000

  17. Solution GL3 V1 = V2 T1 T2 1. If final T is higher than initial T, final V is (greater) than the initial V. 2. If final V is less than initial V, final T is (lower) than the initial T. Lecture PLUS Timberlake 2000

  18. V and T Problem A balloon has a volume of 785 mL on a Fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon? Lecture PLUS Timberlake 2000

  19. VT Calculation Complete the following setup: Initial conditions Final conditions V1 = 785 mL V2 = ? T1 = 21°C = 294 K T2 = 0°C = 273 K V2 = _______ mL x __ K = _______ mL V1 K Check your answer: If temperature decreases, V should decrease. Lecture PLUS Timberlake 2000

  20. Learning Check GL4 A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL? 1) 443°C 2) 170°C 3) - 82°C Lecture PLUS Timberlake 2000

  21. Solution GL4 A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL? 2) 170°C T2 = 291 K x 640 mL = 443 K 420 mL = 443 K - 273 K = 170°C Lecture PLUS Timberlake 2000

  22. Gay-Lussac’s Law: P and T The pressure exerted by a confined gas is directly related to the temperature (Kelvin) at constant volume. P (mm Hg) T (°C) 936 100 761 25 691 0 Lecture PLUS Timberlake 2000

  23. Learning Check GL5 Use Gay-Lussac’s law to complete the statements below: 1. When temperature decreases, the pressure of a gas (decreases or increases). 2. When temperature increases, the pressure of a gas (decreases or increases). Lecture PLUS Timberlake 2000

  24. Solution GL5 1. When temperature decreases, the pressure of a gas (decreases). 2. When temperature increases, the pressure of a gas (increases). Lecture PLUS Timberlake 2000

  25. PT Problem A gas has a pressure at 2.0 atm at 18°C. What will be the new pressure if the temperature rises to 62°C? (V constant) T1 = 18°C T2 = 62°C P1 = 2.0 atm P2 = ? Lecture PLUS Timberlake 2000

  26. PT Calculation P1 = 2.0 atm P2 = ? T1 = 18°C + 273 T2 = 62°C + 273 = 291 K = 335 K What happens to P when T increases?______ Complete: P2 = 2.0 atm x K = atm K Lecture PLUS Timberlake 2000

  27. PT Calculation P1 = 2.0 atm T1 = 18°C + 273 = 291 K P2 = ? T2 = 62°C + 273 = 335 K What happens to P when T increases? P increases (directly related to T) P2 = P1 x T2 T1 P2 = 2.0 atm x 335 K = 2.3 atm 291 K Lecture PLUS Timberlake 2000

  28. Learning Check GL6 Complete with 1) Increases 2) Decreases 3) Does not change A. Pressure _____, when V decreases B. When T decreases, V _____. C. Pressure _____ when V changes from 12.0 L to 24.0 L (constant n and T) D. Volume _____when T changes from 15.0 °C to 45.0°C (constant P and n) Lecture PLUS Timberlake 2000

  29. Solution GL6 A. Pressure 1) Increases, when V decreases B. When T decreases, V 2) Decreases C. Pressure 2) Decreases when V changes from 12.0 L to 24.0 L (constant n and T) D. Volume 1) Increases when T changes from 15.0 °C to 45.0°C (constant P and n) Lecture PLUS Timberlake 2000

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