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Chapter 5

Chapter 5. Gases. General Gas Properties. What are the general properties of all gases?. Take on the shape and volume of the container Can be compressed Mix well together Low densities. Pressure of a Gas. Why do gases exert internal pressure?.

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Chapter 5

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  1. Chapter 5 Gases

  2. General Gas Properties • What are the general properties of all gases? Take on the shape and volume of the container Can be compressed Mix well together Low densities

  3. Pressure of a Gas Why do gases exert internal pressure? Gas molecules will push against any surface they come into contact with because they are always moving

  4. Pressure of a Gas How is pressure defined? • Units: • Pascals (Pa) • Atmospheres (atm) • mm of Hg (mmHg) • Torr (torr)

  5. Pressure of a Gas What is the difference between pressure and atmospheric pressure? Atm. pressure is the external pressure exerted by the atmosphere due to gravity Changes based on location, elevation temperature and weather

  6. Pressure of a Gas • What device measures atmospheric pressure? • Barometer • (atmosphere) • Manometer • (non-atmosphere)

  7. Volume of a Gas What is the volume of a gas? • A measure of the amount of space that gas particles occupy • Units: • Liters (L) or cubic decimeters (dm3) • Milliliters (mL) or cubic centimeters (cm3)

  8. Temperature of a Gas What is the temperature of a gas? • A measure of the amount of energy that the gas particles possess • Directly related to kinetic energy (and thus the velocity) of the gas particles • Units: • Degrees Fahrenheit (°F) • Degrees Celsius (°C) • Kelvin (K)

  9. Relationships What is the difference between direct and indirect relationships? Indirect – as the ind. variable increases, the dep. variable decreases and vice versa Direct – as the ind. variable increases, the dep. variable increases and vice versa Constant means the value doesn’t change

  10. P-V Relationship With temperature (T) constant, what is the relationship between the change in pressure (P) and volume (V)? Why?

  11. V-T Relationship With P constant, what is the relationship between the change in T and V? Why?

  12. P-T Relationship With V constant, what is the relationship between the change in T and P? Why?

  13. Moles With T and P constant, what was the relationship between the change in the moles (n) and the V?

  14. Combining Everything • V α 1/P (Boyle) • V α T (Charles) • P α T (Amonton) • V α n (Avogadro) • We combine them to form an all-in-one proportion: • V α T/P • n will be added later • What are all of the gas law proportions?

  15. Combined Gas Law What is the combined gas law? • Relationship between pressure, volume and temperature of a fixed amount of gas • P1 V1 = P2 V2 T1 T2 P = pressure (atm) V = volume (L) T = temperature (kelvin)

  16. STP • STP = Standard Temperature and Pressure • T = 273 K • P = 1 atm What does STP stand for?

  17. Combined Gas Law Ex. 1 – The gas in an aerosol can is at a pressure of 3.00 atm at 25°C. Directions on the can warn the user not to keep the can in a place where the temperature exceeds 52°C. What would the gas pressure in the can be at 52°C? P1= 3.00 atm T1=25°C + 273 = 298K P2 = ? T2 = 52°C + 273 = 325K Because volume doesn’t change, we leave it out of the formula: P1V1 = P2V2P1 = P2 T1 T2 T1 T2 3.00 atm = P2 298K 325K 3.27 atm = P2

  18. Combined Gas Law • Ex. 2 – A helium-filled balloon has a volume of 50.0L at 25°C and 1.08 atm. What volume will it have at 0.855 atm and 10°C? • V1 = 50.0 L • T1 = 298 K • P1 = 1.08 atm • V2 = ? • T2 = 283 K • P2 = 0.855 atm (1.08 atm)(50.0L) = (0.855 atm)V2 298K 283K 0.181 L = (0.00302) V2 59.9 L = V2

  19. Combined Gas Law Ex. 3 – The volume of a gas is 27.5 mL at 22°C and 0.974 atm. What will the volume be at 15°C and 0.993 atm? Ex. 4 – The volume of a gas at 27°C and 0.200 atm is 80.0 mL.What volume will the same gas sample occupy at STP (1 atm at 0°C)? 0.0000908 L = (0.00345) V2 (0.974atm)(0.0275 L) = (0.993 atm) V2 (295 K) (288 K) 0.0263 L = V2 0.0000533 L = (0.00366) V2 (0.200 atm)(0.0800 L) = (1 atm)V2 (300. K) (273 K) 0.0146 L = V2

  20. Combined Gas Law Ex. 5 – A gas occupying 75 mL at STP is heated to 17°C while the pressure is reduced to 0.97 atm. What is the new volume occupied by the gas? Ex. 6 – What pressure is required to reduce 60.0 mL of a gas at standard conditions to 10.0 mL at a temperature of 25°C? 0.00027 = ( 0.0033) V2 (1 atm)(0.075 L) = (0.97 atm) V2 (273 K) (290. K) 0.082 L = V2 (1 atm)(0.0600 L) = P2 (0.0100 L) (273 K) (298 K) 0.000220 atm = P2 (0.0000336) 6.55 atm = P2

  21. Combined Gas Law Ex. 7 – An empty spray can at room temp (20°C) is thrown onto a bombfire where the temperature reaches 500.°C. If the gas inside the can was initially at a pressure of 1.0 atm, what pressure did it reach in the bombfire right before it exploded? Ex. 8 – The temperature within a car tire at the beginning of a long trip is 25°C. At the conclusion of the trip, the tire has a pressure of 1.80 atm. What is the final Celsius temperature with the tire if its original pressure as 1.75 atm? *Volume doesn’t change, leave it out. 0.0034 atm = P2 / 773 1.0 atm = P2 (293 K) (773 K) 2.6 atm = P2 1.75 atm = 1.80 atm (298 K) T2 T2 = 306K – 273K = 33.5°C

  22. Combined Gas Law Ex. 10 – A sample of gas in a closed container at a temperature of 100°C and a pressure of 3.0 atm is heated to 300°C. What pressure does the gas exert at the higher temperature? Ex. 11 – A sample of gas at 47°C and 1.03 atm occupies a volume of 2.20L. What volume would this gas occupy at 107°C and 0.789 atm? 0.0080 atm = P2 573 3.0 atm = P2 (373 K) (573 K) 4.6 atm = P2 0.00708 L = (0.00208) V2 (1.03 atm)(2.20 L) = (0.789 atm) V2 (320. K) (380. K) 3.40 L = V2

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