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Gases

Gases. Kinetic Molecular Theory. Particles in an ideal gas… have no volume . have elastic collisions. are in constant , random, straight-line motion . don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature. K = ºC + 273. ºF. -459. 32. 212.

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Gases

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  1. Gases

  2. Kinetic Molecular Theory • Particles in an ideal gas… • have no volume. • have elastic collisions. • are in constant, random, straight-line motion. • don’t attract or repel each other. • have an avg. KE directly related to Kelvin temperature.

  3. K = ºC + 273 ºF -459 32 212 ºC -273 0 100 K 0 273 373 Temperature= how fast the molecules are moving • Always use absolute temperature (Kelvin) when working with gases. C. Johannesson

  4. Standard Temperature & Pressure 0°C 273 K 1 atm 101.3 kPa -OR- STP STP

  5. V = volume = how much space a gas occupies Units • L, mL, cm3 • 1000 mL = 1 L, 1 mL = 1 cm3 n = moles = how much gas there is R = ideal gas constant • = 0.0821 (L*atm) (mol*K) • = 8.31 (L*kPa) (mol*K)

  6. V T P BASIC GAS LAWS

  7. V T Charles’ Law • T  V (temperature is directly proportional to volume) • T ↑ V↑ & T↓ V↓ • V1 = V2 T1 T2T is always in K • P and n = constant • Ex)A 25 L balloon is released into the air on a warm afternoon (42º C). The next morning the balloon is recovered on the ground. It is a very cold morning and the balloon has shrunk to 22 L. What is the temperature? 240 K, 33 °C

  8. P V Boyle’s Law • P↓ V ↑ & P↑ V ↓ • P  1/V (pressure is inversely proportional to volume) • P1V1 = P2V2 • T and n = constant Ex: Pressure: 0.98 atm  0.92 atm Volume: ? mL  8.0 L 7.5 L

  9. AVOGADRO’S LAW • Vn Vn • V n (direct) • V1 = V2 n1 n2 • T & P Constant EX: A 3 liter sample of gas contains 3 moles. How much gas will there be, in order for the sample to be 2.3 liters? P & T do not change 2.3moles

  10. P T Gay-Lussac’s Law • P1 = P2 T1 T2 • V & n constant • Direct relationship • PT PT 

  11. Example: A can of Dust Off is sitting next to my computer at 25°C and 3.5 atm. I flip the can over and spray some air out. The room has a pressure of 1.0 atm. What is the temperature of the air as it escapes the container? 85 K, - 188 °C http://www.youtube.com/watch?v=4qe1Ueifekg 2.06 min

  12. COMBINED IDEAL GAS LAW • P1V1 = P2V2 n1T1 n2T2 • If P, V, n, or T are constant then they cancel out of the equation. • n usually constant (unless you add or remove gas), so • P1V1 = P2V2 T1 T2

  13. Ideal Gas Law (“Pivnert”) • PV = nRT • R = ideal gas constant • = 0.0821 (L*atm) (mol*K) • = 8.31 (L*kPa) (mol*K)

  14. Ideal Gas Law (“Pivnert”) PV=nRT R = The Ideal Gas Constant (memorize) R = 0.0821 (L*atm) (mol*K) R = 8.31 (L*kPa) (mol*K) * Choose which R to used based on the units of your pressure. If you have mmHg change it to atm. * V has to be in Liters, n in Moles, T in Kelvin, P can be in atm or kPa P V = n R T (atm) (L) = (moles) (L*atm/mol*K) (K) (kPa) (L) = (moles) (L*kPa/mol*K) (K)

  15. Dalton’s Law of Partial Pressure • The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. • Ptotal = Pgas 1 + Pgas 2 + P­gas 3 + … • Example: Find the total pressure for a mixture that contains three gases. The partial pressure of nitrogen is 15.75 kPa, helium is 47.25 KPa, and oxygen is 18.43 kPa. 81.43 kPa

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