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Behavior of Gases

Behavior of Gases. Ch 12 – Prentice Hall. Kinetic Theory. • Gases are composed of SMALL, SEPARATE particles called MOLECULES. • Gas molecules are in CONSTANT MOTION • All COLLISIONS between particles are PERFECTLY ELEASTIC

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Behavior of Gases

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  1. Behavior of Gases Ch 12 – Prentice Hall

  2. Kinetic Theory • Gases are composed of SMALL, SEPARATE particles called MOLECULES. • Gas molecules are in CONSTANT MOTION • All COLLISIONS between particles are PERFECTLY ELEASTIC • The MOLECULES of a gas display no ATTRACTION or REPULSION for one another.

  3. Kinetic Theory • The AVERAGE KINETIC ENERGY of the molecules is DIRECTLY PROPORTIONAL to the KELVIN temperature of the gas.

  4. Ideal Gas • Gas whose BEHAVIOR conforms to the KINETIC THEORY -it is THEORETICAL.

  5. Gas Pressure: Pressure = FORCE ÷ AREA = ____ atm Atmospheric Pressure - the PRESSURE the earth’s ATMOSPHERE exerts due to its WEIGHT. Barometer: • Instrument used to measure ATMOSPHERIC PRESSURE • Invented by TORRICALLI

  6. The Combined Gas LawCombines the following laws and equations together:

  7. Temperature must be in Kelvin Variation of gas volume with temperature while pressure is kept constant Charles law V1/T1 = V2/T2 T (K) = t (0C) + 273.15

  8. Boyle’sLaw Constant temperature Constant amount of gas P1V1 = P2V2 Pressure and volume units can be any variant of pressure and volume HOWEVER the units MUST agree for both pressures and both volumes!

  9. Combined Gas Law • Expresses the relationship between the PRESSURE, VOLUME and TEMPERATURE of a FIXED amount of GAS. Equation:P1V1 = P2V2 T1 T2

  10. STANDARD TEMPERATURE AND PRESSURE • STP CONDITIONS • 273 K • 1 atm = 760 mmHg

  11. Combined Gas Law Ex: A sample of gas has a volume of 201 L when its temperature is 293 K and its pressure is 224 mmHg. What volume will the gas occupy at STP? V1 = 201 L V2 = ? T1 = 293 K T2 = 273 K P1 = 224 mmHg P2 = 760 mmHg (224) (201) = (760) x (293) (273) (224) (201) (273) = (293) (760) x X = 55 L

  12. Diffusion • The RAPID spreading of a GAS Graham’s Law of Diffusion • Under the same conditions of TEMPERATURE and PRESSURE, gases DIFFUSE at a rate INVERSLEY proportional to the SQUARE ROOT of their DENSITIES (or MOLAR MASS) Equation:

  13. Ideal Gas Equation Equation:PV = nRT • New variables: n = AMOUNT of gas in MOLES R = UNIVERSAL GAS CONSTANT * PROPORTIONALLY constant * value depends on UNITS used for PRESSURE and VOLUME * value of R when using kPa and L R = 8.314 L . kPa / Mol . K

  14. Ex: The average lung capacity for a female student is 3.9 L. At normal body temperature, 37oC, and 110 kPa, how many moles of air could her lungs hold? P = 110 kPa V = 3.9 L T = 310 K (273 + 37) n = X R = 8.314 L . kPa / Mol . K (110)(3.9) = x (310)(8.314) (110)(3.9) = 0.17 mol (310)(8.314)

  15. Avogadro’s Law • Equal VOLUMES of different GASES under the SAME conditions have the SAME number of PARTICLES. • Conversely, if samples of DIFFERENT GASES at the same TEMPERATURE and PRESSURE contain the SAME number of PARTICLES, then the VOLUMES of all the SAMPLES must be EQUAL. • At STP, one MOLE of any gas occupies a VOLUME of 22.4 L. • 22.4 L is the MOLAR VOLUME of a gas.

  16. Dalton’s Law of Partial Pressures Equation: PT = P1 + P2 + P3 … • The PRESSURE of a gas MIXTURE is the SUM of the INDIVIDUAL PRESSURES of each gas ALONE.

  17. • Ex: Oxygen gas has been collected over water at a total pressure of 95.0 kPa and a temperature of 25oC. What is the pressure of the dry oxygen gas? PT = 95 kPa P vapor = 3.17 kPa P oxygen = X 95 = 3.17 + x 91.83 kPa = x

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