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Chapter 17 Kinetic Theory of Gases

Chapter 17 Kinetic Theory of Gases. 17-1,Thermal Equilibrium. If two objects are in thermal equilibrium with a third, then they are in thermal equilibrium with each other Zeroth Law of Thermodynamics. Two objects in thermal equilibrium have the same temperature.

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Chapter 17 Kinetic Theory of Gases

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  1. Chapter 17Kinetic Theory of Gases

  2. 17-1,Thermal Equilibrium

  3. If two objects are in thermal equilibrium with a third, then they are in thermal equilibrium with each other Zeroth Law of Thermodynamics

  4. Two objects in thermal equilibrium have the same temperature

  5. 17-2,Temperature Scales

  6. Celsius Scale • Ice-Point Temperature • Temperature of normal freezing point of water • Steam-point Temperature • Temperature of normal boiling point of water

  7. Celsius Scale • Ice-Point Temperature • Defined to be 0o C • Steam-point Temperature • Defined to be 100o C • Temperature of human body • 37o C

  8. Fahrenheit Scale • Ice-Point Temperature • Defined to be 32o F • Steam-point Temperature • Defined to be 212o F • Fahrenheit-Celsius Conversion • tC = (5/9)(tF – 32o)

  9. 17-3, The Absolute Temperature Scale

  10. Gas Thermometer The volume of the gas in B1 is kept constant by keeping the mercury column in B2 level at the 0 mark. B2 is kept at that level by raising or lowering B3.

  11. Gas Thermometer The height h is a measure of the pressure of the gas in B1. The change in pressure of the gas is a measure of the change in the temperature of the gas

  12. Gas Thermometer It is found that the temperature measured using different gases is the same provided that the gas density is sufficiently low.

  13. Gas Thermometer All gas thermometers extrapolate to the same temperature at zero pressure

  14. Triple Point of Water This is a unique, and reproducible, state in which water, water vapor and ice can coexist. This occurs at P = 4.58 mmHg t = 0.01o C

  15. Triple Point of Water The ideal-gas temperature scale is defined so that the temperature of the triple point of water is 273.16 kelvins (K)

  16. Triple Point of Water Ideal-Gas Temperature Scale P3 pressure at triple point

  17. 17-4The Ideal-Gas Law

  18. Ideal Gas Law The pressure times the volume of a low density gas, at constant temperature, is constant. Robert Boyle (1627-1691)

  19. Ideal Gas Law Further experimental results by Jacques Charles (1746-1823) and Joseph Gay-Lussac (1778-1850) showed that The constant C must be proportional to number of gas molecules N since doubling the volume, with P and T constant, will double C

  20. Ideal Gas Law We can therefore write and therefore k is called Boltzmann’s constant and found to have the value k = 1.381 x 10-23 J/K for all gases.

  21. Ideal Gas Law We often measure the amount of gas in moles. A mole (mol) of gas contains Avogadro’s number NA of atoms or molecules Avogadro’s number NA = 6.022 x 1023 is the number of carbon atoms in 12g of 12C

  22. Ideal Gas Law n moles of gas contains atoms or molecules. Therefore where R is the gas constant

  23. Results for Real Gases

  24. Ideal Gas Law The law is approximately true for real gases at low pressure and density. An ideal gas is defined as a gas that obeys this law exactly.

  25. Ideal Gas Law

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