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Bellringer 3/25

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  1. Bellringer 3/25 • 1. Direct or indirect (inverse) relationship? • A. temp and volume • B. temp and pressure • C. volume and pressure • 2. What type of relationship does this graph display? • 3. What is pressure?

  2. Ch 13 Gases

  3. 13.1 Properties of Gases • Pressure defn– force in an area – for gas – how much force particles of gas exert in area (like on a container)

  4. Pressure Which shoes create the most pressure?

  5. Barometer – measures atmospheric pressure • Hg barometer dial barometer

  6. 3. Atmospheric pressure a. results from massive air being pulled towards center of earth by gravity – weight of air b. changes in weather causes atm p to change c. atm p varies with altitude

  7. B. Units of Pressure 1. standard pressure = 1 atm (atmosphere) 2. conversions 1 atm = 760.0 mm Hg = 760.0 torr (torr from Torrecelli inventor of barometer) Pascal (Pa) is SI (international unit) 1 atm = 101,325 Pa = 101.325 kPa 1 atm = 14.7 psi, pounds / square inch

  8. Summary: • *1atm = 760 mm Hg = 760 torr = 14.7 psi 101.3 kPa • * = add to notecard

  9. 3. Ex: 1.2 atm is how many torr? 1.2 atm 760.0 torr 1 atm = 912 torr How many kPais this? 912 torr 1 atm 101.3 kPa 760.0 torr 1 atm = 122 kPa OR 1.2 atm 101.3 kPa 1 atm = 122 kPa

  10. Parameters (factors) that affect gas behavior • Pressure • Temperature • Volume • Number of particles

  11. Bellringer 3/26 • 1. What type of relationship do pressure and volume have? • 2. What kind of relationship does this graph show? • 3. What will happen if you put a hot can of air into cold water? (see demo)

  12. Boyles Law • Relates pressure and volume – indirect • As one increases, the other decreases B. Eqn: *p1V1= p2V2 C. Temp and number of particles are held constant – same D. Units of pressure – atm, mm Hg, torr, psi, kPa E. Units of volme - liter (l), ml or cm3

  13. E. Ex: Freon used to be used as a refrigerant, but is being replaced. Consider a 1.5 L sample of freon at 56 torr. If the pressure is changed to 150 torr, what volume will the gas occupy? p1V1 = p2V2 (56 torr) (1.5 L) = (150 torr) V2 V2 = 0.56 L  analyze – as inc p, voldec

  14. Charles Law • Relates volume and temp • Direct relationship – as one inc, so does the other • pressure and number of particles are held constant • Eqn: *V1= V2 T1 T2

  15. V T • Volume vs temp

  16. D. Absolute zero 1. temp in which all motion stops 2. zero kelvin (0 K) 3. -273 ºC 4. MUST USE K FOR GAS LAWS! 5. conversion K = ºC + 273

  17. For fun • Did you hear about the man who got cooled to absolute zero? • He’s 0K now.

  18. F. Common temp – FYI ~20ºC is room temp ~37ºC is body temp G. STP – Standard Temp and Pressure Temp = 0ºC or 273K pressure = 1 atm (or conversions of)

  19. E. ex: A 2.0 L sample of air is collected at 298K and is cooled to 5ºC. What is the volume at lower temp? must use K K = ºC + 273 K = 5º C + 273 = 278 K V1 = V2 T1 T2 2.0 L = V2 298K 278K V2 = 1.9 L analyze – cooled, so volume dec?

  20. Bellringer • 1.Sketch a graph for volume vs pressure • 2. Sketch a graph for temp vs volume • 3. What will happen to pressure if you increase temp? • 4. What is the new volume of oxygen gas at 40°C if originally the gas was 1.5L at 20°C? • 1.60 L

  21. Gay-Lussac’s Law number of particles and V are constant P and T are directly proportional. If one temperature goes up, the pressure goes up! *P1 P2 = T1 T2

  22. Ex: A container of oxygen gas at 25°C and 1.05 atm is put into a chamber at 80°C, what will the pressure be now? • p1 = p2 • T1 T2 • 1.05 atm= p2 • 298 K 353K • 1.24 atm analyze inc temp, p inc?

  23. Combined Gas Law • Relates p, V and T. - so combines Boyles and Charles laws. • Number of particles is held constant • *Eqn: p1V1 = p2V2 T1 T2

  24. D. ex: A tire has a volume of 2.5 L at 0.982 atm and 15ºC. What will happen to the volume if the pressure is increased to 0.990 atm and temp increased to 80ºC? p1V1 = p2V2 T1 T2 (0.982 atm) (2.5L) = (0.990 atm) (V2) 288 K 353 K V2 = 3.03 L

  25. Bellringer • 1. What are 3 units of pressure? • 2. how many liters in 250 ml? • 3. What type of relationship do temp and pressure have? • 4. Name 3 gases in the air we breathe

  26. The Ideal Gas Law A. ideal gas law – is the mathematical relationship among pressure, volume, temp, and the number of moles of a gas B. *eqn: pV = nRT C. Deals with amount – the mole (n) D. R is the ideal gas constant R = 0.0821 L.atm / mol . K (note units!)

  27. E. EX. What is the pressure in atmospheres exerted by a 0.500 mole sample of nitrogen gas in a 10.0L container at 298K ? pV = nRT p(10.0L) = (0.500mole)(0.0821 L.atm / mol .K) (298K) p = 1.22 atm

  28. Dalton’s Law of Partial Pressures • partial pressure – the pressure of each gas in a mixture • Dalton’s Law of Partial Pressures – total pressure of a gas is the sum of the partial pressures of the component gases • air pressure is the sum of all the gases • eqn: PTotal = P1 + P2 + P3 . . .

  29. EX; If a container has oxygen molecules that are exerting 2.4 atm of pressure, nitrogen is exerting 5.3 atm and helium exerts 737 mm Hg. What is the total pressure of the container? • PTotal= P1 + P2 + P3 . . . • All need to be same unit 737 mm Hg 1 atm 760 mm Hg = 0.968 atm • PTotal = 2.4 atm + 5.3 atm + 0.968 atm • PTotal= 8.67 atm

  30. bellringer • 1.

  31. Gases collected by Water Displacement • lab procedure • gas is not pure from this procedure - due to water mix with gas C. vapor pressure - caused by liquid evaporating D. to determine pressure of a gas in water displacement procedure: • Ptotal = Pgas + PH2O • PH2O depends on temp (p 467)

  32. E. EX: A sample of potassium chlorate, KClO3, was heated in a test tube. The gas was collected by water displacement at 22°C eqn: 2 KClO3 (s) 2 KCl(s) + 3 O2 (g) The total pressure of water and oxygen was 754 mm Hg and volume of 0.650 L. Calculate the pressure of O2. See chart. Ptotal = Pgas + PH2O 754 mm Hg = PO2 + 19.8 mm Hg PO2 = 734 mm Hg

  33. Bellringer 4/10 • What is the ideal gas constant? • Balance the following equations: • Calcium and HCl produces? • Calcium carbonate decomposes into calcium oxide and carbon dioxide • Hydrochloric acid reacts with magnesium.

  34. Molar Volume of a Gas A. 1 mole of anything has 6.02x1023 molecules (or atoms) B. standard molar volume of a gas – the volume occupied by one mole of a gas at STP 1 mole of gas at STP = 22.4 L C.EX: What volume does 0.0685 mol of gas occupy at STP? • 0.0685 mol 22.4 L • 1 mole • = 1.53 L

  35. Gas Stoichiometry • Can do stoichiometry with gases – use 22.4L = 1 mole to convert • Recall, to do stoichiometry, need balanced equation and use unit conversion (ladder)

  36. C. EX: Propane, C3H8, is a gas that is sometimes used as a fuel for cooking and heating. The complete combustion of propane occurs according to the following balanced eqn: C3H8(g) + 5O2 (g) 3CO2 (g) + 4H2O (g) a. What will be the volume in liters of oxygen required to complete the combustion of 0.350L of propane? • 0.350L C3H8 1 mole C3H8 5 mole O2 22.4 L O2 • 22.4 L C3H8 1mol C3H8 1 mole O2 • = 1.75L

  37. b. What mass of CO2 would be produced? 0.350L C3H8 1 mole C3H8 3 moles CO2 44 g CO2 • 22.4 L C3H8 1mol C3H8 1 mole O2 = 2.06 g CO2