0330prelabanswersexpt3Fall-2011 - Experiment 3: How Can...

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Unformatted text preview: Experiment 3: How Can Solubility be used to Determine Thermodynamic Values of KNO 3 ? PRELABORATORY QUESTIONS 1. Describe the major features of the van’t Hoff plot you will construct. For the dissolution of a salt, do you expect the y-intercept of the best-fit line to be positive or negative? Explain your predictions. Explain the physical implications of the sign of the slope of the line and of the y-intercept. The data should give a straight line with slope = - Δ H°/R and y-intercept = Δ S°/R for the reaction. When a salt dissolves, the ions are no longer constrained in a crystal lattice. Therefore the Δ S° should be positive, and the y-intercept of the line should be positive. An exothermic dissolution will exhibit a positive slope (negative Δ H , while an endothermic reaction will show a negative slope (positive Δ H°). 2. Figure 1 illustrates fictitious van’t Hoff plots for unspecified reactions. Indicate all the possible types of reaction (from the following choices) that each van’t Hoff plot could characterize: vaporization, dissolution of a salt, dissolution of a concentrated acid, precipitation, metathesis, the collision of several gaseous molecules to produce a smaller number of molecules. Explain your choices. (A) Δ H° positive, Δ S° positive: vaporization, dissolution of a salt (B) Δ H° negative,...
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This note was uploaded on 11/05/2011 for the course CHEM 0330 taught by Professor Rose-petruck during the Fall '08 term at Brown.

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0330prelabanswersexpt3Fall-2011 - Experiment 3: How Can...

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