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Unformatted text preview: Version 093 Homework 2 Fakhreddine (53605) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 1.0 points Consider an insulated system containing 437 g of water at 25 C. Adding 185 g of ice at- 10 C will result in equilibrium conditions with how many grams of ice at 0.0 C? Correct answer: 59 . 7 g. Explanation: 002 1.0 points For a hypothetical substance X, the triple point is at Y C and Z atm and the critical point of X is at G C and H atm. Liquid X is less dense than solid X. Which of the following statements about the substance X is NOT true? A phase diagram sketch may be useful. 1. At a pressure between Z atm and H atm, the boiling point of X would be greater than Y C and less than G C. 2. At a pressure somewhat above Z atm, the melting point of X would be fairly close to Y C. 3. At pressures higher than Z atm, we can cause X to sublime if we raise the temperature carefully enough. correct 4. At Y C and Z atm, we would have solid X, liquid X and gaseous X in equilibrium. 5. Liquid X cannot exist at temperatures lower than Y C, regardless of pressures. Explanation: 003 1.0 points Arrange the molecules CCl 4 , SiCl 4 , CH 4 , SiBr 4 in order of increasing molar enthalpy of va- porization. Hint: the molecular mass of SiBr 4 is higher than SiCl 4 . 1. SiBr 4 , SiCl 4 , CCl 4 , CH 4 . 2. CCl 4 , SiCl 4 , CH 4 , SiBr 4 . 3. CH 4 , CCl 4 , SiCl 4 , SiBr 4 . correct 4. SiBr 4 , SiCl 4 , CH 4 , CCl 4 . Explanation: In general, the heavier the molecule, the more energy is required to get that molecule into the gas phase, and the higher the boiling point; and the greater the molar enthalpy of vaporization. 004 1.0 points If you melt an ionic solid, it conducts electric- ity because 1. positive ions move in one direction and negative ions in the opposite direction. cor- rect 2. negative ions move. 3. positive ions move. 4. only electrons are free to move. 5. positive and negative ions move to- gether. Explanation: 005 1.0 points Water causes many electrolytes to dissociate 1. because the dispersion forces between ion and solvent are strong. 2. because water molecules are dipoles and the dipoles orient in an energetically favorable manner to solvate the ions. correct 3. because of repulsive interactions between ions in the crystalline state. 4. because it undergoes hydrogen bonding to large halide ions. Version 093 Homework 2 Fakhreddine (53605) 2 Explanation: The more negative end of the water molecule orients toward the cation and the more positive end orients toward the anion; the ions remain apart....
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This note was uploaded on 04/15/2009 for the course CH 53625 taught by Professor Fakhreddine during the Spring '09 term at University of Texas at Austin.
- Spring '09