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Kinetic Theory of Gases

Kinetic Theory of Gases. consists of small particles that move rapidly in straight lines. essentially no attractive (or repulsive) forces. are very far apart. very small volumes compared volume of container occupied kinetic energies increase with increased temperature.

andrew-mcdowell
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Kinetic Theory of Gases

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  1. Kinetic Theory of Gases • consists of small particles that • move rapidly in straight lines. • essentially no attractive (or repulsive) forces. • are very far apart. • very small volumes compared • volume of container occupied • kinetic energies • increase with increased temperature.

  2. Properties that describe a gas • four properties: pressure (P), volume(V), temperature(T), and amount(n).

  3. What is gas pressure? • force acting on a specific area. Pressure (P) = Force Area • units of atm, mm Hg, torr 1 atm = 760 mm Hg 1 atm = 760 torr

  4. What is atmospheric pressure? • pressure exerted by a column of air • from top of atmosphere • to surface of earth • 1 atmosphere at sea level • depends on altitude and weather • lower at high altitudes • density of air less. • higher on a rainy day • than sunny day

  5. What is a barometer? • measures pressure exerted by • gases in atmosphere. • indicates by • height in mm of mercury column.

  6. Boyle’s Law (pressure-volume) law • pressure of a gas • inversely related to its volume • when T and n are constant • volume decreases • pressure increases • product P x V constant • as long as T and n unchanged P1V1 = P2V2 (T, n constant) • can be solved for any factor

  7. Breathing, an example • During inhalation • lungs expand • pressure in lungs decreases • air flows towards lower pressure in lungs • During exhalation • lung volume decreases • pressure within lungs increases • air flows from higher pressure in lungs to outside

  8. Calculation with Boyle’s Law Freon-12, CCl2F2, is used in refrigeration systems. What is the new volume (L) of a 8.0 L sample of Freon gas initially at 550 mm Hg after its pressure is changed to 2200 mm Hg at constant T? 1. Set up a data table: Conditions 1 Conditions 2 P1 = 550 mm Hg P2 = 2200 mm Hg V1 = 8.0 L V2 = ?

  9. Calculation with Boyle’s law (continued) 2. When pressure increases, volume decreases. Solve Boyle’s Law for V2: P1V1 = P2V2 V2 = V1 x P1 P2 V2 = 8.0 L x 550 mm Hg = 2.0 L 2200 mm Hg

  10. Learning Check For a cylinder containing helium gas indicate if cylinder A or cylinder B represents the new volume for the following changes (n and T are constant). 1) pressure decreases 2) pressure increases

  11. Learning Check A sample of oxygen gas has a volume of 12.0 L at 600. mm Hg. What is the new pressure when the volume changes to 36.0 L? (T and n constant). A) 200. mm Hg B) 400. mm Hg C) 1200 mm Hg

  12. Solution A) 200. mm Hg Data table Conditions 1 Conditions 2 P1 = 600. mm Hg P2 = ??? V1 = 12.0 L V2 = 36.0 L P2 = P1 x V1 V2 = 600. mm Hg x 12.0 L 36.0 L = 200. mm Hg

  13. Charles’ law temperature -volume • Charles’ Law, • Kelvin temperature of a gas • directly related to volume • P and n are constant • temperature of a gas increases • volume increases • V1 T1= V2 T2 • (P and n constant) • rearranging Charles’ Law

  14. Calculations using charles’ law A balloon has a volume of 785 mL at 21°C. If the temperature drops to 0°C, what is the new volume of the balloon (P constant)? 1. Set up data table: Conditions 1 Conditions 2 V1 = 785 mL V2 = ? T1 = 21°C = 294 K T2 = 0°C = 273 K Kelvin (K) temperature in gas calculations.

  15. Calculations Using Charles’ Law (continued) 2. Solve Charles’ law for V2: V1 = V2 T1 T2 V2 = V1 x T2 T1 V2 = 785 mL x 273 K = 729 mL 294 K

  16. Learning Check A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. At what temperature (in °C) will the volume of the oxygen be 640 mL (P and n constant)? 1) 443°C 2) 170°C 3) - 82°C

  17. What is STP? volumes of gases can be compared at STP, Standard Temperature and Pressure, • the same temperature. • Standard temperature (T) • 0°C or 273 K • the same pressure. • Standard pressure (P) • 1 atm (760 mm Hg)

  18. What is Molar volume? • standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, its molar volume • used to form conversion factors 22.4 L and 1 mole 1 mole 22.4 L

  19. Partial Pressure (Dalton’s Law) • pressure of each gas in mixture. • pressure gas would exert if • itself in container • pressure depends on total number of gas particles • not on types of particles • total pressure exerted by gases mixture • sum of partial pressures of gases • Calculate the sum of the partial pressures. Ptotal = PO2 + PHe Ptotal = 342 mm Hg + 855 mm Hg = 1197 mm Hg

  20. Scuba Diving-! • When a scuba diver dives, • increased pressure causes N2(g) to dissolve in blood. • If diver rises too fast, • dissolved N2 will form bubbles in blood • "the bends" • Helium, does not dissolve in blood, • mixed with O2 to prepare breathing mixtures for deep descents.

  21. Gases We Breathe • contains N2 and O2 & small amounts of other gases • O2 enters blood, while CO2 from • blood released • tissues, O2 enters cells, • release CO2 into blood. • O2 flows into tissues • partial pressure of O2 higher in blood, • lower in tissues • CO2 flows out of the tissues • partial pressure of CO2 is higher in tissues, • lower in the blood

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