110_Fa11_LUZ-Review10_26 (1) - When the temperature is...

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Review 10/26 1. Which of the following compounds has the lowest vapor pressure at 25°C? OH HO OH HO OH CH 3 OH OH OH A. C. B. E. D. Solution: Given structural formula, to find the compound with the lowest vapor pressure 1. At the same temperature, compound with the strongest intermolecular forces has the lowest vapor pressure. 2. All five choices have similar types of intermolecular forces: the London dispersion forces, dipole-dipole forces, and Hydrogen bonding. A has the most –OH groups and the heaviest molecular weight, so A has the strongest intermolecular forces. As a result, A has the lowest vapor pressure. ! Answer: A Review 10/26 2. The phase diagram of a substance is given below.
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Unformatted text preview: When the temperature is raised from 20 C to 45 C at 0.8 atm pressure, what phases will be observed during this temperature change? A. solid " liquid B. solid " gas C. liquid " gas D. solid " liquid " gas E. gas only Solution: 1. From the phase diagram, we see that w represents solid phase, x represents liquid phase, y represents gas phase, and z represents triple point. 2. At 0.8 atm and 20 C, the substance falls in the region of x (liquid phase). At 0.8 atm and 45 C, the substance falls in the region of y (gas phase). Therefore, C is correct answer. ! Answer: C...
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This note was uploaded on 01/18/2012 for the course CHEM 110 taught by Professor Hofmann,brucerob during the Fall '08 term at Pennsylvania State University, University Park.

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