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Ch. 10 Physical Characteristics of Gases

Ch. 10 Physical Characteristics of Gases. 10.1 Kinetic Molecular Theory. The Kinetic Molecular Theory. based on the idea that particles are constantly moving can be applied to solid, liquid, or gas provides a model of ideal gas behavior so only an approximation

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Ch. 10 Physical Characteristics of Gases

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  1. Ch. 10 Physical Characteristics of Gases 10.1 Kinetic Molecular Theory

  2. The Kinetic Molecular Theory • based on the idea that particles are constantly moving • can be applied to solid, liquid, or gas • provides a model of ideal gas behavior so only an approximation • When applied to gases, there are 5 assumptions (ie. IDEAL GAS)

  3. 1. Gases consist of tiny particles that are very far apart • most volume is empty space • low density • allows gases to be easily compressed

  4. 2. All collisions between particles and container walls are elastic • there is no net loss of energy when particles collide • total kinetic energy stays constant • energy can be transferred between particles

  5. 3. Particles are in continuous, rapid, random motion • since they are moving, they have KE • KE overcomes their attractive forces

  6. 4. No forces of attraction or repulsion • like billiard balls • bounce apart immediately, do not stick together

  7. 5. Average kinetic energy depends on temperature • KE increases as temperature increases • KE = ½mv2 • where m = mass of particle • where v = velocity of particle • so at the same T, lighter particles have higher speeds than heavier ones

  8. Ideal vs. Real Gases • Ideal gases are defined according to the KMT • Real gases do not behave exactly according to the KMT

  9. Real vs. Ideal Gases • most gases behave close to the ideal when • high temperature – so they have enough KE to overcome attractive forces • low pressure – so they are very spread out • Gases with little attraction are more ideal (monatomic gases)

  10. Ch. 10 Physical Characteristics of Gases 10.2 Pressure

  11. Pressure • P = force per unit area on a surface • Newton – SI unit for force (1 kg*m/s2)

  12. Pressure • As surface area decreases, pressure increases • Pressure exerted by a gas depends on • volume • temperature • number of molecules

  13. Measuring Pressure • barometer • instrument used to measure atmospheric pressure • first one created by Torricelli in early 1600s • Read about it on p. 310

  14. Measuring Pressure • manometer: • measures pressure of gas in a container • gas has less pressure than atmosphere if the Hg is closer to chamber • gas has more pressure than atmosphere if the Hg is further from chamber

  15. Units of Pressure • millimeters of mercury (mmHg) • from mercury barometer • torr (torr) • atmosphere of pressure (atm) • Pascal (Pa) = 1N/m2 (SI unit)

  16. Conversions 1 atm = 760 mmHg = 760 torr = 101.325 kPa

  17. Practice Conversions • Convert 0.927 atm to • mmHg • torr • kPa

  18. Practice Conversions • Convert 148.6 kPa to • atm • mmHg • torr

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