Back
- Carbon tetrachloride, CCl4, and chloroform, CHCl3, are common organic liquids. Carbon tetrachloride’s normal boiling point is 77 °C; chloroform’s normal boiling point is 61 °C. Which statement is the best explanation of these data? (a) Chloroform can hydrogen-bond, but carbon tetrachloride cannot. (b) Carbon tetrachloride has a larger dipole moment than chloroform. (c) Carbon tetrachloride is more polarizable than chloroform.
Problem 3
- If 42.0 kJ of heat is added to a 32.0-g sample of liquid meth-ane under 1 atm of pressure at a temperature of -170°C, what are the final state and temperature of the methane once the system equilibrates? Assume no heat is lost to the surroundings. The normal boiling point of methane is -161.5 °C. The specific heats of liquid and gaseous methane are 3.48 and 2.22 J/g-K, respectively. [Section 11.3]
Problem 4
Problem 5a
Using this graph of CS2 data, determine (a) the approximate vapor pressure of CS2 at 30°C,
Problem 6b
The molecules
have the same molecular formula (C3H8O) but different chemical structures. (b) Which molecule do you expect to have a larger dipole moment? [Sections 11.2 and 11.5]
Problem 7b
The phase diagram of a hypothetical substance is
(b) What is the physical state of the substance under the following conditions? (i) T = 150 K, P = 0.2 atm; (ii) T = 100 K, P = 0.8 atm; (iii) T = 300K, P = 1.0atm. [Section 11.6]
Problem 8a
At three different temperatures, T1, T2, and T3, the molecules in a liquid crystal align in these ways:
(a) At which temperature or temperatures is the substance in a liquid crystalline state? At those temperatures, which type of liquid crystalline phase is depicted?
- In Table 11.3, we saw that the viscosity of a series of hydrocarbons increased with molecular weight, doubling from the six-carbon molecule to the ten-carbon molecule. (c) The surface tension of the hydrocarbon liquids in Table 11.4 does increase from hexane to decane, but only by a rather small amount (20% overall, compared to the doubling of viscosity). Which of the statements below is the most likely explanation for this phenomenon? (i) The flexibility of the molecules has a much larger effect on viscosity than on surface tension. (ii) Viscosity only depends on molecular weight, but surface tension depends on molecular weight and on intermolecular forces. (iii) Larger molecules can make larger liquid droplets and therefore have lower surface tension.
Problem 9
Problem 9a
List the three states of matter in order of (a) increasing molecular disorder
Problem 10a
(a) How does the average kinetic energy of molecules com- pare with the average energy of attraction between mole- cules in solids, liquids, and gases?
Problem 10c
(c) What happens to a gas if you put it under extremely high pressure?
- As a metal such as lead melts, what happens to (a) the average kinetic energy of the atoms? (b) the average distance between the atoms?
Problem 11
- At room temperature, Si is a solid, CCl4 is a liquid, and Ar is a gas. List these substances in order of (b) increasing boiling point.
Problem 12
Problem 13c
At standard temperature and pressure, the molar volumes of Cl2 and NH3 gases are 22.06 and 22.40 L, respectively. (c) The densities of crystalline Cl2 and NH3 at 160 K are 2.02 and 0.84 g/cm3, respectively. Calculate their molar volumes.
Problem 13d
At standard temperature and pressure, the molar volumes of Cl2 and NH3 gases are 22.06 and 22.40 L, respectively (d) Are the molar volumes in the solid state as similar as they are in the gaseous state? Explain.
Problem 15a
(a) Which type of intermolecular attractive force operates between all molecules?
Problem 15b
(b) Which type of intermolecular attractive force operates only between polar molecules?
Problem 15c
(c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?
- Which is generally stronger, intermolecular interactions or intramolecular interactions?
Problem 16
Problem 16b
(b) Which of these kinds of interactions are broken when a liquid is converted to a gas?
Problem 18a,d
Which type of intermolecular force accounts for each of these differences? (a) CH3OH boils at 65 °C; CH3SH boils at 6 °C. (d) Acetone boils at 56 °C, whereas 2-methylpropane boils at -12 °C.
Problem 18b,c
Which type of intermolecular force accounts for each of these differences? (b) Xe is a liquid at atmospheric pressure and 120 K, whereas Ar is a gas under the same conditions. (c) Kr, atomic weight 84 amu, boils at 120.9 K, whereas Cl2, molecular weight about 71 amu, boils at 238 K.
Problem 19
(a) List the following molecules in order of increasing polar- izability: GeCl4, CH4, SiCl4, SiH4, and GeBr4. (b) Predict the order of boiling points of the substances in part (a).
Problem 20b
True or false: (b) For the noble gases the dispersion forces decrease while the boiling points increase as you go down the column in the periodic table.
Problem 20e
True or false: (e) The larger the atom, the more polarizable it is.
Problem 21a
Which member in each pair has the greater dispersion forces? (a) H2O or H2S,
Problem 21b,c
Which member in each pair has the greater dispersion forces? (b) CO2 or CO, (c) SiH4 or GeH4.
Problem 22
Which member in each pair has the stronger intermolecular dispersion forces? (a) Br2 or O2 (b) CH3CH2CH2CH2SH or CH3CH2CH2CH2CH2SH (c) CH3CH2CH2Cl or (CH3)2CHCl
- Rationalize the difference in boiling points in each pair: (a) HF (20 °C) and HCl (-85 °C) (b) CHCl3 (61 °C) and CHBr3 (150 °C) (c) Br2 (59 °C) and ICl (97 °C)
Problem 26
Problem 27a
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (a) Explain why replacement of a hydrogen on the oxygen by a CH3 group generally results in a lower boiling point.
Problem 27b
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (b) What are the major factors responsible for the difference in boiling points of the two ethers?