Name: Date: Grade. Work Session # 12: Intermolecular Forces

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1 Name: Date: Grade Work Session # 12: Intermolecular Forces All questions below must be answered during the lab. Show all work and express your answers with appropriate units and the correct number of significant figures. Q1. Distinguish between intermolecular and intramolecular forces. The term: supramolecular bonding is sometimes used to describe one these forces. Which one? Explain. Q2. When water boils, which of the forces - intermolecular or intramolecular - is being broken? Explain. Q3. When an electric current is run into water, electrolyzing water into H2 and O2, which of these forces - intermolecular or intramolecular - is being broken? Q4. In solid NaCl, there is one kind of force holding the crystal together. In solid H2O, there are two kinds of forces within the crystal. Identify the forces and explain. [Consider your answers in Q2 and Q3.] CHEM- 01A - Work Session # 12: Intermolecular Forces 1

2 Q5. Q6. Q7. From the summary of the bonding and nonbonding (intermolecular) forces in the text, make a generalization about the energy required to separate molecules (as in boiling) compared to the energy required to disassociate ionic substances (as in electrolysis). Molecules of ethane (CH3CH3) and octane (CH3CH2CH2CH2CH2CH2CH2CH3) are held together by relatively weak London (dispersive) forces. However, ethane is a gas a room temperature, whereas octane is a liquid. Explain. Identify the intermolecular forces holding the following molecules together in the solid state. Based on their intermolecular forces, rank the molecules in order of increasing boiling point (1 = lowest, 7 = highest). Confirm your answer with a reference text and cite your resource. Intermolecular forces Molecule CH3NH2 F2 NOF C2H6 H2O I- Cl Na+(aq) Fe2+ & O2(g) Melting Point CHEM- 01A - Work Session # 12: Intermolecular Forces 2

3 Q8. Consider the following molecules. a) CH 3CH 2OCH 3 b) CH 3NH 2 c) HCl d) CH 3COOH A) Which of the following can make intermolecular hydrogen bonds? B) For the molecule(s) that can make hydrogen bonds, draw the molecular structures and show the hydrogen bonding. Q9. Fill in the two hydrogen bonds on the A=T Watson- Crick base pair. CHEM- 01A - Work Session # 12: Intermolecular Forces 3

Q10. Use Figure below to answer the following: (a) Does it take more heat to melt 12.0 g of CH 4 or 12.0 g of Hg? (b) Does it take more heat to vaporize 12.0 g of CH 4 or 12.0 g of Hg? (c) What is the principal intermolecular force in each sample?

4 Q10. Use Figure below to answer the following: (a) Does it take more heat to melt 12.0 g of CH 4 or 12.0 g of Hg? (b) Does it take more heat to vaporize 12.0 g of CH 4 or 12.0 g of Hg? (c) What is the principal intermolecular force in each sample? Q11. The boiling point of ethanol at 1atm is 78.3 C. What is the approximate boiling point of ethanol at 0.5atm? CHEM- 01A - Work Session # 12: Intermolecular Forces 4

5 Q12. Consider the following heating curve. A) Label the ΔH fus and ΔH vap. B) What formula can you use to calculate the energy between points C- D? (Hint: review CH6.) Q13. From the data below, calculate the total heat (in J) needed to convert g of ice at 6.00 C to liquid water at C: mp at 1 atm= 0.0 C, ΔH fus= 6.02 kj/mol c liquid= 4.21 J/g C c solid= 2.09 J/g C Q14. From the data below, calculate the total heat (in J) needed to convert mol of gaseous ethanol at 300 C and 1 atm to liquid ethanol at 25.0 C and 1 atm: bp at 1 atm=78.5 C ΔH vap: 40.5 kj/mol c gas= 1.43 J/g C c liquid= 2.45 J/g C CHEM- 01A - Work Session # 12: Intermolecular Forces 5

6 Q15. Sulfur dioxide is produced in enormous amounts for sulfuric acid production. It melts at 73 C and boils at 10. C. Its ΔH fus is kj/mol and its ΔH vap is kj/mol. The specific heat capacities of the liquid and gas are J/g K and J/g K, respectively. How much heat is required to convert kg of solid SO 2 at the melting point to a gas at 60. C? Q16. A liquid has a ΔH vap of 35.5 kj/mol and a boiling point of 122 C at 1.00 atm. What is its vapor pressure at 113 C? Q17. What is the ΔH vap of a liquid that has a vapor pressure of 621 torr at 85.2 C and a boiling point of 95.6 C at 1 atm? CHEM- 01A - Work Session # 12: Intermolecular Forces 6

7 Q19. Consider the phase diagram to answer the following questions. a) At constant pressure (along the dotted line), indicate the likely physical states as temperature is increased. b) On the phase diagram above, segment corresponds to the conditions of temperature and pressure under which the solid and the gas of the substance are in equilibrium. A) AB B) AC C) AD D) CD E) BC c) On the phase diagram above, segment corresponds to the conditions of temperature and pressure under which the liquid and the gas of the substance are in equilibrium. A) AB B) AC C) AD D) CD E) BC d) On the phase diagram above, segment corresponds to the conditions of temperature and pressure under which the solid and the liquid of the substance are in equilibrium. A) AB B) AC C) AD D) CD E) BC e) On the phase diagram above, the coordinates of point correspond to the triple point. A) A B) B C) C D) D E) E f) On the phase diagram above, the coordinates of point correspond to the critical point. A) A B) B C) C D) D E) E CHEM- 01A - Work Session # 12: Intermolecular Forces 7

Sample Exercise 11.1 Identifying Substances That Can Form Hydrogen Bonds

Sample Exercise 11.1 Identifying Substances That Can Form Hydrogen Bonds In which of these substances is hydrogen bonding likely to play an important role in determining physical properties: methane (CH