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Chem288_2005_Prelim_II_Guide

# Chem288_2005_Prelim_II_Guide - Chemistry 288 Preliminary...

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Chemistry 288 Preliminary Exam II Study Guide Spring 2005, Marohn GUIDELINES AND COVERAGE In order to do well on the exam, you should be able to set up the homework problems without referring to the textbook . Preliminary Exam II will cover lectures 11 through 21 and homeworks 6 through 8, inclusive. I will give you a lot of formulas on the exam. The formulas-and-constants page from the exam appears at the end of this study guide. You should memorize the boxed equations appearing in this study guide. NONELECTROLYTE SOLUTIONS Chang 7.1 – 7.7 We began discussing nonelectrolyte solutions by considering the free energy of mixing, Δ G mix = nRT ( x 1 log x 1 + x 2 log x 2 , ) where x 1 and x 2 are mole fraction. At what mole fraction is the free energy of mixing a maximum? What approximations were involved in deriving Δ G mix ? We next considered binary mixtures of volatile liq- uids and concerned ourselves with the compositions of the liquid and the vapor above the liquid. At equilibrium the chemical potential of a component must be equal to the chemical potential of the same component in the gas. The chemical potential of component 1 in the solu- tion is expressed in terms of the chemical potential of the liquid in the pure state and the vapor pres- sures of the liquid in solution and in the pure state: μ 1 ( l ) = μ 1 ( l ) + RT ln ( P 1 P 1 ) For ideal solutions, we have P 1 = x 1 P 1 This is Raoult’s law. In an ideal solution, all inter- molecular forces are equal, not necessarily zero. In a binary mixture, the solvent usually satisfies Raoult’s law, while the solute follows Henry’s law instead: P 2 = Kx 2 = K m We then used Raoult’s law to consider the vapor- liquid equilibrium between two volatile substances, for example, benzene and toluene. We derived the pressure-composition diagram – see Figure 7.9 on

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Chem288_2005_Prelim_II_Guide - Chemistry 288 Preliminary...

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