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Unformatted text preview: Chem 161-2006 Chapter 11 Hill & Petrucci Homework Problems Chapter 11 problems: 1,5,7,10,11,17,21,23,25,27,31,35,37,39,43,47,49,53,56,57,58,59,63,65,67,69,73,83,90,98,99 Self-Assessment Questions 1. What is meant by (a) a condition of dynamic equilibrium, (b) the triple point of a substance, (c) the critical point of a substance, (d) a dispersion force? (a) A microscopic condition at which molecules of reactant (or one phase) become product (or a second phase), while molecules of product (the second phase) become reactant (or the first phase), but, from a macroscopic point of view, neither the concentrations of reactants nor products (or phases) change. In order to have dynamic equilibrium, the forward and reverse processes must occur at equal rates. (b) The triple point is that point in a phase diagram in which the three phases (e.g., solid, liquid and gas) coexist. (c) The critical point is that point in a phase diagram, above which, the gas and liquid cannot coexist as two phases. (d) A dispersion force, also known as a London force, or a London dispersion force, is the force between two molecules resulting from a dispersion of the electrons from one side of the molecule to the other side, so that non-polar molecules would be instantaneously polar. 5. Of these quantities, the one that we expect to be largest for a substance (expressed in kJ/mol) is which of the following? (a) molar heat capacity of a liquid (b) enthalpy of fusion (c) enthalpy of vaporization (d) enthalpy of sublimation It takes a lot of energy to break bonds. Many bonds are broken in going from a solid to a gas (enthalpy of sublimation), certainly more than going from a solid to a liquid (fusion) or from a liquid to a gas (vaporization). Heat capacity of a liquid is not breaking bonds; it is simply increasing the kinetic energy. Hence, enthalpy of sublimation is the largest. 7. If the triple-point pressure of a substance is greater than 1 atm, we expect which of the following? (a) the solid to sublime without melting (b) the boiling-point temperature to be lower than the triple-point temperature (c) the melting point of the solid to come at a lower temperature than the triple point (d) that the substance cannot exist as a liquid (a) True. The phase diagram shows that at 1 atm the solid goes directly to a gas, if the triple-point is greater than 1 atm. (b) False. At 1 atm. there would be no boiling point since the substance would never exist as a liquid. (c) False. At 1 atm. there would be no melting point since the substance converts directly from a solid to a liquid. (d) True. At 1 atm. there is no liquid phase. (My answer disagrees with the Solutionss Manual answer.) 10. Of the compounds HF, CH 4 , CH 3 OH, and N 2 H 4 , hydrogen bonding as an important intermolecular force is expected in which of these?...
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- Spring '11