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Unformatted text preview: 245 Chapter 14 Solutions The emphasis in this chapter is on the physical properties common to all solutions, not on their chemical prop-erties. The latter depend on the chemicals themselves. Learning Objectives In this chapter, you should keep in mind the following goals. 1 To learn how the random motions of molecules tend to lead naturally to the spontaneous mixing of a solute with a solvent. 2 To learn how intermolecular attractive forces, such as dipole-dipole attractions, ion-dipole attractions and hydrogen bonds, can affect to the ability of a solute to dissolve in a solvent. 3 To learn how the like-dissolves-like rule helps us qualitatively predict whether a solution can be made. 4 To learn how the heat of solution for a solid dissolving in a liquid is the net effect of lat-tice energies and heats of solvation. 5 To learn how the relative strengths of intermolecular attractions in two liquids affect their heat of solution. 6 To learn how the effect of temperature on solubility correlates with the sign of the heat of solution. 7 To learn how to apply Henry’s law in calculations. 8 To learn the general response to pressure of any equilibrium between a saturated solution of a gas in a liquid. 9 To learn how to work problems involving weight percentage concentration and molal concentration. 10 To learn how to convert a concentration in one set of units to another set. 11 To learn how solutes affect the vapor pressure of a solution and to use the Raoult's law equation. 12 To learn how a nonvolatile solute elevates the boiling point and depresses the freezing point of a solution and how the data involved in these changes can be used to calculate a molecular mass. 13 To learn how osmotic pressure data can be used to determine molecular masses. 14 To learn that the colligative properties of solutions of ionic compounds depend not just on the molality in terms of the formula units of the compound but on the number of ions into which the compound breaks up in solution. 15 To learn the chief physical characteristics of colloidal dispersions and to see how particle size is the key factor in understanding the differences among solutions, colloidal disper-sions, and suspensions. 246 Solutions 14.1 Substances mix spontaneously when there is no energy barrier to mixing Review When two substances are in contact, the random motions of their molecules tend to cause them to mix. In the absence of forces to prevent this, mixing occurs and the substances dissolve in one another. We can also view the mixed and unmixed states in terms of their relative probabilities once the two are in contact, as we do here for two gases. The mixed state has a vastly higher probability than the unmixed one, so the system changes spontaneously from a state of low probability to one of high probability. This illustrates a general principle of nature: a system, left to itself, will tend toward the most probable state....
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This note was uploaded on 04/07/2008 for the course CHEM 102 taught by Professor Bush during the Spring '07 term at UMBC.
- Spring '07