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Ideal Gases and the Compressibility Factor

A high pressure, molecules are more influenced by repulsive forces. V real > V ideal  Z > 1. The effect of molecular attraction causes: V real < V ideal  Z < 1. Ideal Gases and the Compressibility Factor. 1 mol, 300K for various gases. Lower temperatures

stephanie-hull
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Ideal Gases and the Compressibility Factor

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  1. A high pressure, molecules are more influenced by repulsive forces. Vreal > Videal  Z > 1 The effect of molecular attraction causes: Vreal < Videal  Z < 1 Ideal Gases and the Compressibility Factor 1 mol, 300K for various gases

  2. Lower temperatures Little thermal motion of molecules Attractive forces dominate: Vreal < Videal  Z < 1 Higher temperatures More influenced by repulsive forces: Vreal > Videal  Z > 1 Effect of Pressure on Compressibility Factor CH4, various temperatures

  3. Comparing Various Equations of State Ethane, 400K van der Waals Redlich-Kwong Peng-Robinson Solid line – experimental

  4. Ammonia B2V = -0.142 dm3 mol-1 at 373 K Ideal gas 1.000 Z 373 K slope = B2P(T) = B2V(T)/RT 0.998 0.1 0 P / bar Second Virial Coefficient and Intermolecular Potentials The second virial coefficient is the most important. Can be determined by plotting Z vs. P.

  5. The effect of temperature At high T B2V increases Boyle temperature: Temperature at which B2V(T) = 0. Repulsive and attractive interactions cancel and gas behaves ideal

  6. The Lennard-Jones Potential Contributions: Dipole-dipole (including H-bonding) Induced dipole London dispersion attraction The short range 1/r12 repulsive term The long range 1/r6 attractive term u(r)/ε 0 ε r/σ 0 1 2 3

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