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- Explain why the enthalpy of vaporization of vanadium (460 kJ/mol) is much larger than that of zinc (114 kJ/mol).
Problem 75
- Tell what is meant by each of the following terms. (c) Band gap
Problem 77
- Classify the following semiconductors as n-type or p-type. (a) Si doped with In (b) Ge doped with Sb (c) Gray Sn doped with As
Problem 86
- Arrange the following materials in order of increasing electrical conductivity. (a) Cu (b) Al2O3 (c) Fe (d) Pure Ge (e) Ge doped with In
Problem 90
- Considering only electronegativity, rank the LED semiconductors made of solid solutions in order of increasing bandgap energy. Al0.40Ga0.60As, Al0.25Ga0.75As, Al0.05Ga0.95As
Problem 101
Problem 102a
A photovoltaic cell contains a p–n junction that converts solar light to electricity. (a) Silicon semiconductors with a band-gap energy of 107 kJ/mol are commonly used to make photovoltaic cells. Calculate the wavelength that corresponds to the band-gap energy in silicon.
Problem 103a
A photovoltaic cell contains a p–n junction that that converts solar light to electricity. An optimum semiconductor would have its band-gap energy matched to the wavelength of maximum solar intensity at the Earth's surface. (a) What is the color and approximate wavelength of maximum solar intensity at the Earth's surface? Refer to the figure for Problem 12.102.
Problem 103b
A photovoltaic cell contains a p–n junction that that converts solar light to electricity. An optimum semiconductor would have its band-gap energy matched to the wavelength of maximum solar intensity at the Earth's surface. (b) Which of the following semiconductors absorb at a wavelength matched with maximum solar intensity? CdTe with a band-gap energy of 145 kJ/mol or ZnSe with a band-gap energy of 248 kJ/mol.
- Gallium arsenide, a material used to manufacture laser printers and compact disc players, has a band gap of 130 kJ/mol. Is GaAs a metallic conductor, a semiconductor, or an electrical insulator? With what group 4A element is GaAs isoelectronic? (Isoelectronic substances have the same number of electrons.)
Problem 104
- What is the coordination environment of the K+ ions in the fullerene-based superconductor K3C60?
Problem 112
- Looking at Figure 12.27 identify the coordination numbers of the Cu, Y, and Ba atoms.
Problem 113
Problem 115
The YBa2Cu3O7 superconductor can be synthesized by the solgel method from a stoichiometric mixture of metal ethoxides followed by heating in oxygen. How many grams of Y(OCH2CH3)3 and how many grams of Ba(OCH2CH3)2 are required to react with 75.4 g of Cu(OCH2CH3)2 and an excess of water? Assuming a 100% yield, how many grams of YBa2Cu3O7 are obtained?
- Why are oxide ceramics more corrosion-resistant than metals?
Problem 119
- Silicon nitride 1Si3N42, a high-temperature ceramic useful for making engine components, is a covalent network solid in which each Si atom is bonded to four N atoms and each N atom is bonded to three Si atoms. Explain why silicon nitride is more brittle than a metal like copper.
Problem 120
- Describe the reactions that occur when an Si1OH24 sol becomes a gel. What is the formula of the ceramic obtained when the gel is dried and sintered?
Problem 126
- Explain why graphite/epoxy composites are good materials for making tennis rackets and golf clubs.
Problem 132
- Explain why silicon carbide–reinforced alumina is stronger and tougher than pure alumina.
Problem 133
- The mineral magnetite is an iron oxide ore that has a density of 5.20 g/cm³. At high temperature, magnetite reacts with carbon monoxide to yield iron metal and carbon dioxide. When 2.660 g of magnetite is allowed to react with sufficient carbon monoxide, the CO₂ product is found to have a volume of 1.136 L at 298 K and 751 mm Hg pressure. (a) What mass of iron in grams is formed in the reaction? (b) What is the formula of magnetite?
Problem 134
Problem 136a
A group 3A metal has a density of 2.70 g/cm3 and a cubic unit cell with an edge length of 404 pm. Reaction of A 1.07 cm3 chunk of the metal with an excess of hydrochloric acid gives a colorless gas that occupies 4.00 L at 23.0 °C and a pressure of 740 mm Hg. (a) Identify the metal.
Problem 137c
A cube-shaped crystal of an alkali metal, 1.62 mm on an edge, was vaporized in a 500.0 mL evacuated flask. The resulting vapor pressure was 12.5 mm Hg at 802 °C. The structure of the solid metal is known to be body-centered cubic. (c) What are the densities of the solid and the vapor in g>cm3?
- Assume that 1.588 g of an alkali metal undergoes complete reaction with the amount of gaseous halogen contained in a 0.500 L flask at 298 K and 755 mm Hg pressure. In the reaction, 22.83 kJ is released 1ΔH = -22.83 kJ2. The product, a binary ionic compound, crystallizes in a unit cell with anions in a face-centered cubic arrangement and with cations centered along each edge between anions. In addition, there is a cation in the center of the cube. (c) Sketch a space-filling, head-on view of the unit cell, labeling the ions. Are the anions in contact with one another?
Problem 138
- Europium(II) oxide is a semiconductor with a band gap of 108 kJ/mol. Below 69 K, it is also ferromagnetic, meaning all the unpaired electrons on europium are aligned in the same direction. How many f electrons are present on each europium ion in EuO? (In lanthanide ions the 4f orbitals are lower in energy than the 6s orbitals.)
Problem 139
Problem 141c
The mineral wustite is a nonstoichiometric iron oxide with the empirical formula FexO, where x is a number slightly less than 1. Wustite can be regarded as an FeO in which some of the Fe sites are vacant. It has a density of 5.75 g>cm3, a cubic unit cell with an edge length of 431 pm, and a facecentered cubic arrangement of oxygen atoms. (c) Each Fe atom in wustite is in either the +2 or the +3 oxidation state. What percent of the Fe atoms are in the +3 oxidation state?
Problem 141d
The mineral wustite is a nonstoichiometric iron oxide with the empirical formula FexO, where x is a number slightly less than 1. Wustite can be regarded as an FeO in which some of the Fe sites are vacant. It has a density of 5.75 g>cm3, a cubic unit cell with an edge length of 431 pm, and a facecentered cubic arrangement of oxygen atoms. (d) Using X rays with a wavelength of 70.93 pm, at what angle would third-order diffraction be observed from the planes of atoms that coincide with the faces of the unit cells? Third-order diffraction means that the value of n in the Bragg equation is equal to 3.
Problem 144a
Small molecules with C=C double bonds, called monomers, can join with one another to form long chain molecules called polymers. Thus, acrylonitrile, H2C=CHCN, polymerizes under appropriate conditions to give polyacrylonitrile, a common starting material for producing the carbon fibers used in composites. (a) Write electron-dot structures for acrylonitrile and polyacrylonitrile, and show how rearranging the electrons can lead to formation of the polymer.
Problem 144b
Small molecules with C'C double bonds, called monomers, can join with one another to form long chain molecules called polymers. Thus, acrylonitrile, H2C'CHCN, polymerizes under appropriate conditions to give polyacrylonitrile, a common starting material for producing the carbon fibers used in composites. (b) Use the bond dissociation energies in Table 7.1 to calculate ΔH per H2C'CHCN unit for the conversion of acrylonitrile to polyacrylonitrile. Is the reaction endothermic or exothermic?