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fall 09 lm _10 real gases

fall 09 lm _10 real gases - Chem 481L Lab Module#10 Due...

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0 ) ( = R U HS = Chem 481L Fall 2009 Lab Module #10 Properties of Real Gases Due Date: Noon, Tuesday, November 17 Submit via Blackboard Goal: To explore the physical properties of real gases in the context of non-negligible intermolecular forces. Research questions: Can real substances be quantitatively modeled by Virtual Substance in the high- density context where intermolecular forces are important? How does VS compare with predictions made by different equations of state and with experimental data? Introduction: Real substances can be described by models that take into account the different types of intermolecular interactions – repulsions as well as attractions – and describe these interactions in different ways. For example, we used the Ideal Gas Law, which assumes no intermolecular forces, to describe noble gases: [1] This week we consider alternative equations of state that use various ways to account for intermolecular forces. Hard-Sphere Model: Another (simplified) model is to describe a gas as a collection of impenetrable "billard" balls of diameter σ. Each atom would then take up a volume of roughly σ 3 , and a collection of N atoms would occupy a volume of Nσ 3 . The volume available to atoms in the box would be reduced by this "excluded" volume. Making this adjustment to the ideal gas law results in: [2] where b is the excluded volume for a particle and nb is the excluded volume for n moles of particles. Unlike the ideal gas model, in this "hard sphere" model there are repulsive intermolecular forces acting between the particles. In classical physics, the force between two atoms can be related to the slope (i.e. derivative) of an intermolecular potential , U(R), where R is the separation between particles. The intermolecular potentials corresponding to the hard sphere model is as follows: for R > σ [3] for R σ
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