Liquids and Intermolecular Forces Practice Problems

1. ________________attractions are bonds that hold compounds together a. What are 2 examples of theses attractions? 2. ________________attractions are between molecules. 3. Which attraction is stronger? 4. Which state of matter will have the strongest intermolecular forces? Which state has the weakest? 5. Order the intermolecular forces (IMF) in order of weakest to strongest: hydrogen bonding, dipole-dipole, iondipole, London dispersion 6. List all the possible IMF for the following compounds: a. HCl b. NH3 c. H2O d. CH4 e. NaCl dissolved in water 7. For each type of compound determine what forces are possible: Type of IMF Atoms Nonpolar molecules Polar molecules Polar molecules Ionic solids without OH, NH, containing OH, dissolved in or HF groups NH, or HF groups polar liquids Dispersion forces Dipole-dipole Hydrogen bonding Ion-dipole Explore the following procedure and complete the subsequent practice exercises in preparation for the synchronous class discussion. Step 1 or Step 2 are review from general chemistry I. Review Lewis structures and molecular polarity if needed. Procedure: Example: CH2Cl2 1. Draw the Lewis structure and 3-D representation of the molecular geometry of the compound. (The lone pairs on external atoms can be omitted for simplification.) 2. Determine if the molecule is polar or nonpolar. 3. If polar, does the molecule contain H-F, O-H, or N-H bonds? If yes, the predominant intermolecular force is hydrogen bonding. If no, the predominant force is dipole-dipole. 4. For nonpolar molecules, the intermolecular force is dispersion forces. Dispersion forces are present in all molecules but are generally weaker than dipole-dipole interactions or hydrogen bonding. The molecule is polar because there is a net resultant dipole. No F-H, O-H, or N-H bonds. The predominant intermolecular force is dipole-dipole. Dispersion forces also contribute to the interaction between dichloromethane molecules but are generally weaker than dipole-dipole interactions. Practice exercises: Follow the procedure given above to determine the predominant (i.e. strongest) intermolecular force for the following molecules. 3-D Predominant Compound Formula Lewis Structure Representation Intermolecular Name and Polarity Force sulfur dioxide SO2 ethyl alcohol C2H5OH (C―C―O backbone) sulfur trioxide SO3 dimethyl ether CH3OCH3 8. Which has stronger forces dimethyl ether, CH3OCH3 or ethanol, CH3CH2OH? List the forces in each compound. 9. IMF affect what properties? 10. The stronger the IMF, the _________ the boiling point. 11. As molar mass increases, boiling point ___________. 12. The stronger the IMF, the ____________the melting point. 13. What does < like dissolves like= mean? 14. The resistance of a liquid to flow is called _______________ 15. Water bugs can walk on water due to surface tension of water, since water has (STRONG OR WEAK) intermolecular forces. 16. Fill in the table with the phase changes corresponding to an endothermic or exothermic process. Endothermic Exothermic 17. Which of the following is exothermic: a. When water is cooled, it turns to ice. a. Wet clothes dry on a warm summer day. b. Frost appears on a window on a cold winter day. 18. How much heat is required to raise 5.00 g of ice from -20.0oC to 50.0oC? Specific Heat of H2O(s) 2.087 J/g oC Specific Heat of H2O(l) 4.184 J/g oC ΔHfus (H2O) 333.6 J/g 19. Calculate the enthalpy change on converting 1.00 mol of ice at -25°C to vapor at 125°C? The specific heats of ice, water and steam are 2.09 J/gK, 4.18 J/gK and 1.84 J/gK, DHfus = 6.01 kJ/mol, and is DHvap = 40.67 kJ/mol. 20. On the phase diagram, describe what is happening at 1) 2) 3) 21. If solid methane at 1 am is heated while pressure is held constant, will it melt or sublime? 22. What equations do you need to know for this chapter that will not be given on the exam?