Ch.11 - Liquids & Phase Changes
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- When ethyl alcohol, CH3CH2OH, dissolves in water, how many hydrogen bonds are formed between one ethyl alcohol molecule and surrounding water molecules? Sketch the hydro- gen bonding interactions. (Hint: Add lone pairs of electrons to the structure before drawing hydrogen bonds.)
Problem 50
- Water at room temperature is placed in a flask connected by rubber tubing to a vacuum pump, and the pump is turned on. After several minutes, the volume of the water has decreased, and what remains has turned to ice. Explain
Problem 52
- Ether at room temperature is placed in a flask connected by a rubber tube to a vacuum pump. The pump is turned on, and the ether begins boiling. Explain why this occurs.
Problem 53
- Benzene has a melting point of 5.53 °C and a boiling point of 80.09 °C at atmospheric pressure. Its density is0.8787 g>cm3 when liquid and 0.899 g>cm3 when solid; it has Tc = 289.01 °C, Pc = 48.34 atm, Tt = 5.52 °C, and Pt = 0.0473 atm. Starting from a point at 200 K and 66.5 atm, trace the following path on a phase diagram. (1) First, increase T to 585 K while keeping P constant. (2) Next, decrease P to 38.5 atm while keeping T constant. (3) Then, decrease T to 278.66 K while keeping P constant. (4) Finally, decrease P to 0.0025 atm while keeping T constant. What is your starting phase, and what is your final phase?
Problem 62
- How many phase transitions did you pass through in Problem 11.62, and what are they?
Problem 64
- Intermolecular forces are important in creating ordered arrangements in liquid crystals. What types of intermolecu- lar forces exist in a sample of the following compound?
Problem 70
Problem 72
Two compounds (labeled I and II) have a liquid crystal state. Predict which compound has a higher temperature associ- ated with the solid to liquid crystal phase change. Explain your reasoning.
- The compound cholesteryl benzoate is a rod-like molecule that undergoes a phase change from the solid to the liq- uid crystal phase at 145.5 °C. When cholesteryl benzoate is mixed with cholesteryl oleyl carbonate, a molecule with a curved shape, the temperature of the solid to liquid crys- tal transition changes. Predict if the transition temperature increases or decreases and explain your reasoning.
Problem 73
- The chlorofluorocarbon refrigerant trichlorofluoromethane, CCl3F, has Pvap = 100.0 mm Hg at -23 °C and ΔHvap = 24.77 kJ>mol. (b) What is ΔSvap for trichlorofluoromethane?
Problem 75
- Substance X has a vapor pressure of 100 mm Hg at its triple point (48 °C). When 1 mol of X is heated at 1 atm pres- sure with a constant rate of heat input, the following heating curve is obtained: (b) For each of the following, choose which phase of X (solid, liquid, or gas) fits the description. (iii) Has the greatest specific heat
Problem 77
- Which of the following substances would you expect to have a nonzero dipole moment? Explain, and show the direction of each. (a) Cl2O (b) XeF4 (c) Chloroethane, CH3CH2Cl (d) BF3
Problem 78
- Draw three-dimensional structures of PCl3 and PCl5, and then explain why one of the molecules has a dipole moment and one does not.
Problem 81
- Of the two compounds SiF4 and SF4, which is polar and which is nonpolar?
Problem 83
- Fluorine is more electronegative than chlorine, yet fluoromethane 1CH3F; m = 1.86 D2 has a smaller dipole moment than chloromethane 1CH3Cl; m = 1.90 D2. Explain.
Problem 85
- What is the difference between London dispersion forces and dipole–dipole forces?
Problem 86
- Which substance in each of the following pairs would you expect to have larger dispersion forces? (b) HCl or HI
Problem 87
- Of the substances Xe, CH3Cl, and HF, which has: (a) The smallest dipole–dipole forces?
Problem 89
- For each of the following substances, identify the intermolecular force or forces that predominate. Using your knowledge of the relative strengths of the various forces, rank the substances in order of their normal boiling points: Al2O3, F2, H2O, Br2, ICl, NaCl.
Problem 91
- 1,3-Propanediol can form intramolecular as well as intermolecular hydrogen bonds. Draw a structure of 1,3-propanediol showing an intramolecular hydrogen bond.
Problem 93
- Dimethyl ether has the following structure.
Problem 95
(b) Which of the following illustrations depicts the hydrogen bonding that occurs between dimethyl ether and water? (i)
(ii)
- Draw a phase diagram showing how the phase boundaries differ for a pure solvent compared with a solution.
Problem 100
- Just as individual bonds in a molecule are often polar, molecules as a whole are also often polar because of the net sum of individual bond polarities. There are three possible structures for substances with the formula C2H2Cl2, two of which are polar overall and one of which is not. (b) Which of the three structures is nonpolar, and which two are polar? Explain.
Problem 114
- Has the Earth's surface experienced warming as a result of increasing levels of greenhouse gases? If so, by how much?
Problem 132
- Propanol (PrOH) and methyl methacrylate (MMA) asso-ciate in solution by an intermolecular force, forming an adduct represented as PrOH•MMA. The equilibrium con- stant for the association reaction is Kc = 0.701 at 298 K. (b) Draw a plausible structure for the PrOH • MMA adduct. Use to signify an intermolecular interaction.
Problem 163