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chemistry
physical chemistry

Questions and Answers of Physical Chemistry

(a) What are the C¬C¬C bond angles in diamond? (b) What are they in graphite?
Employing the bond enthalpy values listed in Table 8.4, estimate the molar enthalpy change occurring upon (a) Polymerization of ethylene,(b) Formation of nylon 6,6,(c) Formation of polyethylene
Although polyethylene can twist and turn in random ways, the most stable form is a linear one with the carbon backbone oriented as shown in the following figure:The solid wedges in the figure
(a) In polyvinyl chloride shown in Table 12.5, which bonds have the lowest average bond enthalpy? (b) When subjected to high pressure and heated polyvinyl chloride converts to diamond. During this
Silicon has the diamond structure (Figure 12.30(a)) with unit cell edge length of 5.43 Å and eight atoms per unit cell. (a) How many silicon atoms are there in of material? (b) Suppose you dope that
KCl has the same structure as NaCl. The length of the unit cell is 6.28 Å. The density of KCl is 1.984 g/cm3, and its formula mass is 74.55 amu. Using this information, calculate Avogadro's number?
Look up the diameter of a silicon atom, in Å. The channel length in a Pentium 4 processor chip is 65 nm long. How many silicon atoms does this correspond to?
Indicate the type of crystal (molecular, metallic, ionic, or covalent-network) each of the following would form upon solidification: (a) InAs (b) MgO (c) HgS (d) In (e) HBr.
(a) Draw a picture that represents a crystalline solid at the atomic level. (b) Now draw a picture that represents an amorphous solid at the atomic level?
Amorphous silica, SiO2, has a density of about 2.2 g/cm3, whereas the density of crystalline quartz is 2.65g/cm3. Account for this difference in densities?
Two patterns of packing different types of spheres are shown here. For each structure(a) Draw the two-dimensional unit cell,(b) Determine the angle between the lattice vectors, g, and whether the
Two patterns of packing different types of spheres are shown here. For each structure(a) Draw the two-dimensional unit cell,(b) Determine the angle between the lattice vectors, g, and whether the
Of the seven three-dimensional primitive lattices, (a) Which hone has a unit cell where the a and b lattice vectors form are c tangular base, while the c lattice vector is perpendicular to the other
(a)What kind of packing arrangement is seen in the accompanying photo?(b) What is the coordination number of each cannonball in the interior of the stack?
Of the seven three-dimensional primitive lattices,(a) Which one has a unit cell where the a and b lattice vectors form abase that is an arbitrary parallelogram (like the unit cell of a
Of the seven three-dimensional primitive lattices, which ones have a unit cell where no two lattice vectors are perpendicular to each other?
What is the minimum number of atoms that could be contained in the unit cell of an element with a body-centered cubic lattice?
What is the minimum number of atoms that could be contained in the unit cell of an element with a face-centered cubic lattice?
The unit cell of nickel arsenide is shown here.(a) What type of lattice does this crystal possess?(b) What is the empirical formula?
The unit cell of a compound containing strontium, iron, and oxygen is shown here.(a) What type of lattice does this crystal possess (all three lattice vectors are mutually perpendicular)?(b) What is
The densities of the elements K, Ca, Sc, and Ti are 0.86, 1.5, 3.2, and 4.5 g/cm3, respectively. What factors are likely to be of major importance in determining this variation? Which factor do you
Which of the following substances would you expect to possess metallic properties: (a) TiCl4, (b) NiCo alloy, (c) W, (d) Ge, (e) ScN?
Consider the unit cells shown here for three different structures that are commonly observed for metallic elements. (a)Which structure(s) corresponds to the densest packing of atoms? (b) Which
Rhenium oxide crystallizes with a structure that has a primitive cubic lattice, as shown here. In the image on the left, the sizes of the ions have been reduced to show the entire unit cell.(a) How
Sodium metal (atomic weight 22.99 g/cm3) adopts a body centered cubic structure with a density of 0.97 g/cm3. (a) Use this information and Avogadro's number (NA = 6.022 × 1023) to estimate the
Iridium crystallizes in a face-centered cubic unit cell that has an edge length of 3.833 Å. (a) Calculate the atomic radius of an iridium atom. (b) Calculate the density of iridium metal?
Calcium crystallizes with a body-centered cubic structure. (a) How many Ca atoms are contained in each unit cell? (b) How many nearest neighbors does each Ca atom possess? (c) Estimate the length of
Aluminum metal crystallizes in a cubic close-packed structure [face-centered cubic cell, Figure 12.14(a)]. (a) How many aluminum atoms are in a unit cell? (b) What is the coordination number of each
An element crystallizes in a body-centered cubic lattice. The edge of the unit cell is 2.86 Å, and the density of the crystal is 7.92 g/cm3. Calculate the atomic weight of the element?
Define the term alloy. Distinguish among solid solution alloys, heterogeneous alloys, and intermetallic compounds?
Distinguish between substitutional and interstitial alloys. What conditions favor formation of substitutional alloys?
For each of the following alloy compositions indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) Fe0.97Si0.03, (b)
For each of the following alloy compositions indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) Cu0.66Zn0.34, (b) Ag3Sn, (c)
Classify each of the following statements as true or false: (a) Substitutional alloys tend to be more ductile than interstitial alloys. (b) Interstitial alloys tend to form between elements with
The electronic structure of a doped semiconductor is shown here.(a) Which band, A or B, is the valence band?(b) Which band is the conduction band?(c) Which band consists of bonding molecular
Classify each of the following statements as true or false: (a) Intermetallic compounds have a fixed composition. (b) Copper is the majority component in both brass and bronze. (c) In stainless steel
Which element or elements are alloyed with gold to make the following types of "colored gold" used in the jewelry industry? For each type indicate what type of alloy is formed: (a) White gold, (b)
What is the chemical composition of purple gold? Is the composition variable? Why don't jewelers use purple gold to make rings or necklaces?
Explain how the electron-sea model accounts for the high electrical and thermal conductivity of metals?
(a) Compare the electronic structures of atomic chromium and atomic selenium. In what respects are they similar, and in what respects do they differ?(b) Chromium is a metal, and selenium is a
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.23. Construct a molecular-orbital diagram for a chain containing six lithium atoms and use
Repeat Exercise 12.45 for a linear chain of eight lithium atoms?
Which would you expect to be the more ductile element, (a) Ag or Mo, (b) Zn or Si? In each case explain your reasoning.
How do you account for the observation that the alkali metals, like sodium and potassium, are soft enough to be cut with a knife?
Explain this trend in melting points: Y 1522 oC, Zr 1852 oC, Nb 2468 oC, Mo 2617 oC?
Shown here are cartoons of two different polymers. Based on these cartoons, which polymer would you expect to be denser? Which one would have the higher melting point?
For each of the following groups which metal would you expect to have the highest melting point; (a) Gold (Au), rhenium (Re), or cesium (Cs); (b) Rubidium (Rb), molybdenum (Mo), or indium (In); (c)
Tausonite, a mineral composed of Sr, O, and Ti, has the cubic unit cell shown in the drawing.(a) What is the empirical formula of this mineral?(b) It is easy to see that Ti is coordinated by six
Rutile is a mineral composed of Ti and O. Its unit cell, shown in the drawing, contains Ti atoms at each corner and a Ti atom at the center of the cell. Four O atoms are on the opposite faces of the
NaF has the same structure as NaCl.(a) Use ionic radii from Chapter 7 to estimate the length of the unit cell edge for NaF.(b) Use the unit cell size calculated in part (a) to estimate the density of
Clausthalite is a mineral composed of lead selenide (PbSe). The mineral adopts a NaCl-type structure. The density of PbSe at 25 oC is 8.27 g/cm3. Calculate the length of an edge of the PbSe unit cell?
A particular form of cinnabar (HgS) adopts the zinc blende structure, Figure 12.26. The length of the unit cell edge is 5.852 Å. (a) Calculate the density of HgS in this form. (b) The mineral
At room temperature and pressure RbI crystallizes with the NaCl-type structure. (a) Use ionic radii to predict the length of the cubic unit cell edge.(b) Use this value to estimate the density.(c) At
CuI, CsI, and NaI each adopt a different type of structure. The three different structures are those shown in Figure 12.26.(a) Use ionic radii, Cs+ (r = 1.81 Å), Na+ (r = 1.16 Å), Cu+ (r = 0.74
The rutile and fluorite structures, shown here (anions are colored green), are two of the most common structure types for ionic compounds where the cation to anion ratio is 1:2.(a) For CaF2 and ZnF2
The coordination number for Mg2+ ion is usually six. Assuming this assumption holds, determine the anion coordination number in the following compounds: (a) MgS, (b) MgF2, (c) MgO.
The accompanying image shows photoluminescence from four different samples of CdTe nanocrystals, each embedded in a polymer matrix. The photoluminescence occurs becausethe samples are being
The coordination number for the AI3+ ion is typically between four and six. Use the anion coordination number to determine the coordination number in the following compounds: (a) AlF3 where the
Classify each of the following statements as true or false: (a) Although both molecular solids and covalent-network solids have covalent bonds, the melting points of molecular solids are much lower
Classify each of the following statements as true or false: (a) For molecular solids the melting point generally increases as the strengths of the covalent bonds increase. (b) For molecular solids
Both covalent-network solids and ionic solids can have melting points well in excess of room temperature, and both can be poor conductors of electricity in their pure form. However, in other ways
Which of the following properties are typical characteristics of a covalent-network solid, a metallic solid, or both: (a) Ductility, (b) Hardness, (c) High melting point?
For each of the following pairs of semiconductors, which one will have the larger band gap: (a) CdS or CdTe, (b) GaN or InP, (c) GaAs or InAs?
For each of the following pairs of semiconductors, which one will have the larger band gap: (a) InP or InAs, (b) Ge or AlP, (c) AgI or CdTe?
For each of the following pairs of semiconductors, which one will have the larger band gap: (a) InP or InAs, (b) Ge or AlP, (c) AgI or CdTe? Discuss.
If you want to dope GaAs to make a p-type semiconductor with an element to replace As, which element(s) would you pick?
Silicon has a band gap of 1.1 eV at room temperature.(a) What wavelength of light would a photon of this energy correspond to?(b) Draw a vertical line at this wavelength in the figure shown, which
Covalent bonding occurs in both molecular and covalent network solids. Why do these two kinds of solids differ so greatly in their hardness and melting points?
Cadmium telluride is an important material for solar cells.(a) What is the band gap of CdTe?(b) What wavelength of light would a photon of this energy correspond to?(c) Draw a vertical line at this
The semiconductor GaP has a band gap of 2.2 eV. Green LEDs are made from pure GaP. What wavelength of light would be emitted from an LED made from GaP?
The first LEDs were made from GaAs, which has a band gap of 1.43 eV. What wavelength of light would be emitted from an LED made from GaAs? What region of the electromagnetic spectrum does this light
GaAs and GaP (Eg = 2.26 eV) make solid solutions that have the same crystal structure as the parent materials, with As and P randomly distributed throughout the crystal. GaPxAs1 -x exists for any
Red light-emitting diodes are made from GaAs and GaP solid solutions, GaPxAs1-x (see Exercise 12.73). The original red LEDs emitted light with a wavelength of 660 nm. If we assume that the band gap
What is a monomer? Give three examples of monomers taken from the examples given in the chapter?
An ester is a compound formed by a condensation reaction between a carboxylic acid and an alcohol. Read the discussion of esters in Section 24.4 and then give an example of a reaction forming an
Write a chemical equation for formation of a polymer via a condensation reaction from the monomers succinic acid (HOOCCH2CH2COOH) and ethylenediamine (H2NCH2CH2NH2)?
Draw the structure of the monomer(s) employed to form each of the following polymers shown in Table 12.5: (a) Polyvinyl chloride, (b) Nylon 6,6, (c) Polyethylene terephthalate?
Silicon is the fundamental component of integrated circuits. Si has the same structure as diamond. Is Si a molecular, metallic, ionic, or covalent-network solid?
Write the chemical equation that represents the formation of(a) polychloroprene from chloroprene (polychloroprene is used in highway-pavement seals, expansion joints, conveyor belts, and wire and
The nylon Nomex®, a condensation polymer, has the following structure:Draw the structures of the two monomers that yield Nomex®.
Proteins are polymers formed by condensation reactions of amino acids, which have the general structureIn this structure, R represents ---- H, ----CH3, or another group of atoms. Draw the general
What molecular features make a polymer flexible? Explain how cross-linking affects the chemical and physical properties of the polymer?
Are high molecular weights and a high degree of crystallinity always desirable properties of a polymer? Explain.
Briefly describe each of the following: (a) Elastomer, (b) Thermoplastic, (c) Thermosetting plastic?
Explain why "bands" may not be the most accurate description of bonding in a solid when the solid has nanoscale dimensions?
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (a) What color is the emitted light? (b) Would
True or false: (a) The band gap of a semiconductor decreases as the particle size decreases in the 1-10-nm range. (b) The light that is emitted from a semiconductor, upon external stimulation,
What kinds of attractive forces exist between particles in (a) Molecular crystals, (b) Covalent-network crystals, (c) Ionic crystals, (d) Metallic crystals?
True or false: If you want a semiconductor that emits blue light, you could either use a material that has a band gap corresponding to the energy of a blue photon or you could use a material that has
Gold adopts a face-centered cubic structure with a unit cell edge of 4.08 Å (Figure 12.11). How many gold atoms are there in a sphere that is 20 nm in diameter? Recall that the volume of a sphere is
Cadmium telluride, CdTe, takes the zinc blende structure (Figure 12.26) with a unit cell edge length of 6.49 Å. There are four cadmium atoms and four tellurium atoms per unit cell. How many of each
A face-centered tetragonal lattice is not one of the 14 threedimensional lattices. Show that a face-centered tetragonal unit cell can be redefined as a body-centered tetragonal lattice with a smaller
Pure iron crystallizes with a body-centered cubic structure, but small amounts of impurities can stabilize a face-centered cubic structure. Which form of iron has a higher density?
Introduction of carbon into a metallic lattice generally results in a harder, less ductile substance with lower electrical and thermal conductivities. Explain why this might be so?
As mentioned in Section 12.3, Ni3Al is used in the turbines of aircraft engines because of its strength and low density. Nickel metal has a cubic close-packed structure with a face-centered cubic
For each of the intermetallic compounds shown in Figure 12.17 determine the number of each type of atom in the unit cell. Do your answers correspond to ratios expected from the empirical formulas:
What type of lattice-primitive cubic, body-centered cubic, or face-centered cubic-does each of the following structure types possess: (a) CsCl, (b) Au, (c) NaCl, (d) Po, (e) ZnS?
Tin exists in two allotropic forms: Gray tin has a diamond structure, and white tin has a close-packed structure. One of these allotropic forms is a semiconductor with a small band gap while the
Rank the contents of the following containers in order of increasing entropy:
The following diagram shows the vapor-pressure curves of a volatile solvent and a solution of that solvent containing a nonvolatile solute. (a) Which line represents the solution? (b) What are the

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