ln3s08 - Lecture 3: Solubility of Gases, Liquids, and...

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Lecture 3: Solubility of Gases, Liquids, and Solids in Liquids Up to this point we have dealt primarily with pure compounds. The next two sets of lectures deal with what happens when mixtures are created. The lectures are in two parts: ! The thermodynamics of what happens when you mix a liquid with a solid, a liquid with a liquid and a liquid with a gas ! The interesting properties that are a consequence of mixing—specifically, colligative properties which are properties that depend only on the relative concentrations of the components. These colligative properties include freezing point depression and boiling point elevation, vapor pressure lowering and osmotic pressure. A bit of nomenclature associated with mixing: A solution is the consequence of mixing two or more compounds A solute is the smaller quantity in the solution A solvent is the larger quantity in the solution For example, sea water is a solution consisting of the solute, NaCl, mixed with the solvent, water. Note difference between sections 8.1 – 8.7 and sections 8.8– 8.13 where we changed phases where we mix phases S " G or L " S S + L or G + L and look at ! G = ! H – T ! S and look at ! G = ! H – T ! S There are some consistent ideas associated with the process of mixing: ! G = ! H – T ! S ? ! G is (–) means that a solid dissolved in solution or that one liquid is miscible with another liquid ! S is always (+) because mixing substances makes mixing always increases the disorder of the system, therefore increasing the entropy of the system so delta S is always positive with the process of mixing
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The complicating issue is the heat of mixing-- ! H can be either endo or exothermic and is quite varied ! H soln is (+) for NaCl in H 2 O ! H soln is (–) for Na 2 SO 4 in H 2 O ! H soln is (–) for O 2 in H 2 O Consider the case that Δ H mix is negative: since Δ S mix is positive then ! G soln will have to be negative and the reaction happens. Now consider the case that Δ H mix is positive: in this case the spontaneity of the reaction is temperature dependence and follows the arguments a outlined in Chapter 7 for temperature dependent reaction spontaneity. For example, if a process is endothermic it can be made spontaneous by
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This note was uploaded on 04/09/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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ln3s08 - Lecture 3: Solubility of Gases, Liquids, and...

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