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Chapter 10

Chapter 10. Physical Characteristics of Gases. Sect. 10-1: The Kinetic-Molecular Theory of Matter. Kinetic-molecular theory (KMT)– based on idea that particles of matter are always in motion Ideal gas – imaginary gas that perfectly fits all assumptions of the KMT. 5 Assumptions of KMT.

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Chapter 10

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  1. Chapter 10 Physical Characteristics of Gases

  2. Sect. 10-1: The Kinetic-Molecular Theory of Matter • Kinetic-molecular theory (KMT)– based on idea that particles of matter are always in motion • Ideal gas – imaginary gas that perfectly fits all assumptions of the KMT

  3. 5 Assumptions of KMT • Gases consist of large # of tiny particles spread far apart relative to their size. • Collisions between particles as well as particle-container collisions are elastic (no kinetic energy lost). • Gas particles are in constant, random motion.

  4. There are no forces of attraction or repulsion between gas particles. • The average kinetic energy of gas particles depends on the temperature of the gas. 2 gases at same temp have same avg. KE. • KE = ½ mv2

  5. KMT and the Nature of Gases • Expansion • Fluidity • Low density • Compressibility • Diffusion and effusion • Diffusion – 2 substances mixing caused by their random motion • Effusion – gas particles pass through tiny opening

  6. Deviation of Real Gases from Ideal Behavior • Real gas – a gas that does not behave completely according to the assumptions of the KMT • Real gases behave close to ideal as long as pressure is not very high and temp is not very low • Real gases do have attractions for each other; the more polar the molecules, the greater the attraction

  7. Sect. 10-2: Pressure • Pressure – force per unit area • Pressure = force area • Barometer – device used to measure atmospheric pressure • Manometer – device used to measure pressure of an enclosed gas sample

  8. Units of pressure • Millimeters of mercury (mm Hg) – common unit of pressure (came from barometer reading) • Torr – equal to 1 mm Hg, named for Torricelli who invented barometer • Atmosphere (atm) – equal to 760 mm Hg • Pascal (Pa) – SI unit of pressure (kilopascals are more common, 1 atm = 101.325 kPa)

  9. Standard temperature and pressure (STP) – 1 atm and 0°C

  10. Volume Pressure Sect. 10-3: The Gas Laws • Boyle’s law – volume is inversely proportional to pressure, as long as temp and amt. of gas are constant P1V1 = P2V2

  11. Volume Temp • Charles’s Law – volume is directly proportional to the Kelvin temperature, when holding amt. of gas and pressure constant V1 = V2 T1 T2

  12. Temp • Gay-Lussac’s Law - pressure is directly proportional to the Kelvin temperature, when holding amt. of gas and volume constant P1 = P2 T1 T2 Pressure

  13. Combined gas law – expresses the relationship between temperature, volume, and pressure of a fixed amount of gas P1 V1 = P2 V2 T1 T2

  14. Partial pressure – the pressure of each gas in a mixture • Dalton’s law of partial pressures – the total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas PT = P1 + P2 + P3 +…

  15. Collecting gas over water • When gases are collected over water, they are always mixed with water vapor, so you must subtract the water vapor pressure from the atmospheric pressure to get the pressure of the gas Patm = Pgas + Pwater

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