# 3NewGases - The Properties of Real Gases Dr Allison J Long...

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1 The Properties of Real Gases Dr. Allison J. Long

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2 7.1 Ideal Gas Laws: Real gases at low pressure and high temperature. Boyle’s Law Charles’s Law Amonton’s Law Avogadro’s Law Ideal Gas Law Constant T, n Variable P, V Constant P, n Variable T, V Constant V, n Variable P, T Constant T, P Variable V, n 2 2 1 1 V P V P = 2 2 1 1 T V T V = 2 2 1 1 T P T P = 2 2 1 1 n V n V = nRT PV =
3 Assumptions made for “ideal” gases: (1)Gas molecules are point masses. In reality these molecules occupy a finite volume so they can’t be compressed to a volume less than the total molecular volume. (2) Gas molecules don’t interact. In reality they do interact (negligible at low densities) Fig 1.6 Potential energy Yellow: ideal gas Dashed blue: approximate r (distance) where a more nearly exact equation of state should be used.

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4 7.2 van der Waals equation of state Redlich-Kwong equation of state ( 29 nRT nb V V a n P = - + 2 2 ( 29 + - - = b V V T a b V RT P m m m 1 a and b are constants for a given gas a and b are constants for a given gas a and b are experimentally determined for a given gas. The parameter “a” is a measure of the strength of the intermolecular potential, and “b” is a measure of the minimum volume that a mole of molecules can occupy. The same symbols are used for both equations, but they have different values for a given gas.
5 Fig 7.1 a and b Yellow: van der Waals Blue: Redlich-Kwong Red: Ideal gas Black dots: accurate values

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6 virial equation of state + + + + = 3 2 ) ( ) ( ) ( 1 V T D V T C V T B RT V P + + + + = 3 2 ) ( ) ( ) ( 1 P T d P T c P T b RT V P Beattie-Bridgeman equation of state ( 29 2 3 2 1 m m m m V A B V T V c V RT P - + - = -
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## This note was uploaded on 09/28/2011 for the course CHEM 3441 taught by Professor Lobue during the Spring '11 term at Georgia Southern University .

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3NewGases - The Properties of Real Gases Dr Allison J Long...

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