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| Understanding the concepts
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Check your answers |
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| 1.
| Open the Densities of the Three States of Water Table on the Web Site. Why is the density of H2O(g) so much smaller than that of H2O(l) or H2O(s)? Characterize some other similarities and differences between the three states of matter.
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| 2.a.
| Go through the Changes of State Understanding Concepts on the CD to review phase changes and heating curves. When a solid converts to a liquid and then to a gas, what happens in terms of the intermolecular forces? Rationalize why  Hvap for water is more than 6 times larger than Hfus.
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| b.
| On the CD, go to the Changes of State Understanding Concepts screen with the heating curve. The heating curve has 5 basic parts to it. There are two plateau regions and three positive sloping lines in a typical heating curve. To calculate the energy necessary to convert some ice at a certain temperature below 0°C to gas at a temperature above 100°C, five quantities must be known: Hvap, Hfus, the specific heat capacity of gaseous water, the specific heat capacity of water, and the specific heat capacity of ice. Match these five quantities to the five parts in a typical heating curve. For H2O at 1 atm, what temperature is the plateau at the lower temperature? the plateau at the higher temperature?
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| c.
| For a challenging question on calculating energy changes, do Problem 13.17 of the text. |
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| 3.a.
| Characterize the difference between intramolecular forces and intermolecular forces. Open the Intermolecular Forces Understanding Concepts on the CD to review types of intermolecular forces for covalent compounds. What types of intermolecular forces do nonpolar covalent compounds exhibit? How is size related to the strength of London dispersion forces? The London dispersion forces-size relationship is illustrated very nicely in the Freezing Points of the Group 8 Elements Table on the Web site. Explain why the freezing points increase from neon to xenon.
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| 3.b.
| What are dipole-dipole forces? A strong type of dipole-dipole force is hydrogen bonding. What three covalent bonds do you look for in order for a covalent compound to exhibit hydrogen bonding? How does the strength of ionic forces compare to hydrogen bonding? With this discussion in mind, how would you expect the melting points of HF, HCl, and NaCl to compare? |
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| 3.c.
| Practice predicting the strongest type of intermolecular forces for various covalent compounds by doing the Exercises in the Understanding Concepts Intermolecular Forces on the CD. For most of the Exercises, you need to know whether the compound is polar or nonpolar. The nonpolar compounds in the Exercise (the compounds that do not have a permanent moment) are: BeH2. BeF2 BF3, BH3, CH4, CCl4, CO2, O3, PF5, SbCl5, SiCl4, and SF6. With this in mind, you should be able to complete the Exercises. |
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| 3.d.
| What is vapor pressure? How is the vapor pressure of a liquid related to the strength of intermolecular forces? Apply this idea by doing Problems 13.36 and 13.38 in the text. |
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| 4.
| Open the Examples of the Various Types of Solids Table on the Web site. What are the differences between ionic, molecular, and atomic solids? How do the melting points of ionic compounds compare to molecular solids? The melting points of atomic solids vary greatly within this classification. Give examples to illustrate this. Review Example 13.4 from Section 13.6 in the text, then do Self-Check Exercise 13.2 to practice identifying types of solids. Finally, do Problem 13.64 in the text to review predicting melting points for various types of solids. |
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| 5.
| Open Key Words on the CD and test your ability to define the important terms presented in Chapter 13. |
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| 6.
| Test your understanding of Chapter 13 by taking the ACE quizzes on the Web site. |
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