Honors Chemistry. Chapter 10: Forces of Attraction, Phase Change, Date / / Period and Solids Answer Key

Transcription

1 Honors Chemistry Name Chapter 10: Forces of Attraction, Phase Change, Date / / Period and Solids Answer Key 1. What is a dipole-dipole attraction? What is hydrogen bonding? Dipole-dipole attractions occur because oppositely charged ends (positive and negative ends) of different molecules attract one another like little magnets. Hydrogen bonding is the strongest type of intermolecular force. It occurs when the highly electronegative elements N, O, F bond with H. These attractions are stronger because as N, O, and F pull the bonding electrons closer to themselves all that is remaining on the H side of the compound is a naked proton. This causes the N, O, or F side to be greatly negative and the H side to be extremely positive. 2. How do the strengths of dipole-dipole forces compare with the strengths of typical covalent bonds? All intermolecular forces are significantly weaker than intramolecular forces; this includes dipole-dipole (an intermolecular force) and covalent bond (an intramolecular force). 3. Explain how London dispersion forces arise. Although London dispersion forces exist among all molecules, for what type of molecules are they the only major intermolecular forces? Are London dispersion forces relatively strong or relatively weak? Explain. All molecules have the potential for the formation of London forces, however, these are the only types of IMF that occurs in a non-polar covalent molecules, Noble gases, and nonmetal atoms. LDF result from the movement of electrons outside of its normal orbit which generates temporary positive and negative regions in the molecule. 4. How do intermolecular forces affect each of the following? a. When intermolecular forces increase the boiling point increases. b. When intermolecular forces increase the melting point increases. c. When intermolecular forces increase vapor pressure decreases. d. Solubility substances with like intermolecular forces dissolve in one another Like Dissolves Like. e. Adhesive forces two different substances attract due to like intermolecular forces. (Example: water in a graduated cylinder) f. Cohesive forces two different substances do not attract due to unlike intermolecular forces. (Example: mercury in a graduated cylinder) 5. What causes dipole-dipole interactions? a. unequally sharing of electron pairs b. bonding of a covalently-bonded hydrogen to an lone electron pair c. the random motion of electrons d. none of these

2 6. Why is hydrogen bonding only possible with hydrogen? a. Hydrogen is the least electronegative element known. b. The size of a hydrogen atom is similar to that of oxygen, nitrogen, and fluorine. c. Hydrogen is the only atom with an unshielded nucleus when it forms covalent bonds. d. More than one of the above. 7. Which of the following is the weakest attractive force? a. polar covalent bond c. ionic bond b. hydrogen bond d. dipole-dipole force 8. What is the strongest intermolecular / intramolecular force present for each of the following compounds? Drawing the geometric structures can help to determine the type of intermolecular forces. a. water Hydrogen bonding b. carbon tetrachloride London dispersion forces c. ammonia Hydrogen bonding d. carbon dioxide London dispersion forces e. phosphorus trichloride Dipole-dipole forces f. nitrogen London dispersion forces g. ethane (C 2 H 6 ) London dispersion forces h. acetone (CH 3 COCH 3 ) Dipole-dipole forces i. methanol (CH 3 OH) Hydrogen bonding j. borane (BH 3 ) LDF 9. Circle all the compounds in the following list that would be expected to form intermolecular hydrogen bonds in the liquid state: a. CH 3 OCH 3 (dimethyl ether) b. CH 4 c. HF d. CH 3 CO 2 H (acetic acid) e. Br 2 f. CH 3 OH (methanol)

3 10. Specify the predominant force of attraction that would affect the boiling point of the compound and list it immediately following the substance. Then in the last column, indicate which member of the pair you would expect to have the higher boiling point. Possible forces of attraction are: metallic bonding, ionic bonding, network covalent bonding, hydrogen bonding, dipole-dipole and London dispersion forces Substance #1 Predominant Intermolecular Force Substance #2 Predominant Intermolecular Force Substance with Higher Boiling Point a. HCl (l) Dipole-dipole I 2 LDF HCl (l) b. CH 3 F Dipole-dipole CH 3 OH Hydrogen bonding CH 3 OH c. H 2 O (l) Hydrogen bonding H 2 S Dipole-dipole H 2 O (l) d. SiO 2(s) Network covalent SO 2 Dipole-dipole SiO 2(s) bonding e. Fe (s) Metallic Bonding Kr LDF Fe f. CH 3 OH (l) Hydrogen bonding CuO (s) Ionic bonding CuO g. NH 3 Hydrogen bonding CH 4 LDF NH 3 h. HCl (g) Dipole-dipole NaCl Ionic bonding NaCl i. SiC Network covalent bonding Cu (s) Metallic Bonding SiC 11. What must be overcome to melt or vaporize a substance? Explain. The forces of attract between the molecules must be at least partially overcome in order for a substance to change state. These forces of attraction are typically intermolecular forces. 12. Define the equilibrium vapor pressure of a liquid. How is the magnitude of a liquid s vapor pressure related to the intermolecular forces? Equilibrium vapor pressure is the pressure caused by the equilibrium of the liquid vaporizing and the gas condensing in a closed system. This is affected by the tendency of the liquid to vaporize and the tendency to vaporization is determined by the strength of the intermolecular forces. 13. How do we know that the properties of the solid and the liquid states of a substance are more similar than to the properties of the substance in the gaseous state? Solids and liquids are more similar because of the interaction of the particles (intermolecular Forces). The particle of solids and liquids interact more identically then particles of liquids and gases because solids and liquids have similar IMF of attraction. 14. Explain how the process of vaporization and condensation represent equilibrium in a closed container. At constant temperature, the liquid is going to the gaseous phase or state at the same rate that the gas is going to the liquid phase or state. 15. What is the effect of a dishwashing liquid on the surface tension of water? Explain. Dishwashing liquid decreases the surface tension of water because the intermolecular forces of the soap are different than the intermolecular forces of water. Because the forces of attraction are different, the addition of the soap weakens the attraction that typically occurs between the water molecules.

4 Phase Diagram For each of the questions on this worksheet, refer to the phase diagram for mysterious compound X. 16. What is the critical temperature of compound X? ~770 o C 17. If you were to have a bottle containing compound X in your closet, what phase would it most likely be in? Extrapolating from this diagram, it s most likely a gas. 18. At what temperature and pressure will all three phases coexist? 350 o C, ~51 atm 19. If I have a bottle of compound X at a pressure of 45 atm and temperature of 100 o C, what will happen if I raise the temperature to 400 o C? It will sublime 20. Why can t compound X be boiled at a temperature of 200 o C? It does not form a liquid at this temperature. It only exists as a liquid at temperatures above 350 o C. 21. If I wanted to, could I drink compound X? No. At the temperatures and pressures that it forms a liquid, you d probably die. 22. What observable difference would there be for the solid/liquid line for the phase diagram for compound X and the phase diagram for water? Why? Refer to your notes/book for a phase diagram of water. The solid / liquid line for compound X angles to the right because the density of the solid state of compound X is denser then the liquid state of compound X. The solid liquid line for water would angle to the left because the density of the solid state of water is less dense then the liquid state of water. 23. What is vaporization? What is condensation? Vaporization it is a substance changing from a liquid phase to a gaseous phase Condensation it is a substance changing from a gaseous phase to a liquid phase.

5 24. Define molar heat of fusion and molar heat of vaporization. The amount of heat (energy) needed to melt (go from a solid to a liquid phase) 1.00 mole of a substance at its melting point. The amount of heat (energy) needed to vaporize 1.00 moles a substance at its boiling point. 25. The heat of fusion of aluminum is 3.95 kj/g. What is the molar heat of fusion of aluminum? 3.95 kj Al g Al = 107 kj/mole g 1 mole Al 26. Calculate the total energy required to convert 55.1 grams of ice at 0.00 o C to a resulting gaseous state at 100. o C. S (solid) = 2.1 J/g o C H fusion = 6.02 kj/mole S (liquid) = 4.2 J/g o C H vaporization = 40.7 kj/mole S (vapor) = 2.1 J/g o C (55.1 grams)(1 mole / g) = 3.06 moles H fusion X moles (6.02 kj/mole)( 3.06 moles) = 18.4 kj Q = s m T (4.2 J/g o C)(55.1 grams) (100. o C) = 23,000 J = 23 kj H vaporization X moles (40.7 kj/mole)( 3.06 moles) = 125 kj 18.4 kj 23 kj kj 166 kj

6 27. Draw a heating / cooling curve for iron, which has a melting point of 1535 o C and a boiling point of 2750 o C. Make sure to properly label both axis of your graph. Types of Solids 28. Crystalline solid a solid characterized by the regular arrangement of its components. 29. List some properties of each of the following. a. Ionic solids components are ions. (NaCl) - Ionic bonds - High melting and boiling points - Hard and brittle - Do not conduct electricity b. Molecular solids components are molecules. (Sucrose C 12 H 22 O 11 ) - D-D, H. Bonding, and/or LDF - Medium to Low melting and boiling points - Soft / hard - Do no conduct electricity (used as insulators) c. Atomic solids components are atoms. - Network Atoms - Compounds containing Si and C(diamond) - Covalent bonds - Hard - High melting and boiling points - Insulators - Metals - delocalized electrons (sea of electrons) - soft to hard - Various melting points - Conduct heat and electricity - Noble gases - LDF - Low melting and Boiling points - Gases d. Alloy a substance that contains a mixture of elements and has metallic properties. - substitutional alloy metal atoms are replaced by other metal atoms of similar size. - Interstitial alloy are formed when some of the holes are filled by smaller atoms.