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Unformatted text preview: Lecture 5: Kinetic Theory of Gases Equation of State • Let’s begin by reviewing some of the variables we can use to describe an object, or a system of objects: – temperature – volume – mass – pressure • All such variables are called state variables – i.e., each one tells us something about the state of the system • There is another set of variables that describe the flow of energy into or out of the system – we’ve discussed one such transfer variable , heat, in the previous lectures Ideal Gases • For a gas, there is no intrinsic “volume” – the gas fills whatever container it’s placed into • An ideal gas is one for which the molecules don’t influence each other much – e.g., a noble gas at low pressure • We can find rules that relate the quantity of gas (in terms of its mass m ) and its pressure, volume and temperature • Actually, it’s often more convenient to express the quantity of gas in moles , defined as: • Turns out there are 6.022 x 10 23 molecules in a mole (Avagadro’s number) n = μ Μ Molar mass (atomic weight expressed in grams) Equation of State for an Ideal Gas • For any gas that is near “ideal” the following equation of state holds: • R is a number that is constant, no matter what type of gas is used – the value of this “universal gas constant” is 8.314 J/mol K • We can also write the equation of state in terms of the number of molecules rather than the number of moles: • k B is “Boltzmann’s constant” (1.38 x 1023 J/K) • Cross check: PV = νΡΤ PV = Νκ Β Τ “Ideal Gas Law” R = 8.314 ϑ μ ολ⋅ Κ × 1μ ολ 6.02 ×10 23 = 1.38 ×1023 ϑ Κ = κ Β Kinetic Theory of Gases • We’ve already given the equation of state for an ideal gas:...
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 Fall '08
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 Thermodynamics, Mass, Kinetic theory

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