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chemistry for engineering students

Questions and Answers of Chemistry For Engineering Students

Manganese has a body-centered cubic unit cell and has a density of 7.88 g/cm3. From this information, determine the length of the edge of the cubic cell.
The spacing in a crystal lattice can be measured very accurately by X-ray diffraction, and this provides one way to determine Avogadro’s number. One form of iron has a body-centered cubic lattice,
How many electrons per atom are delocalized in the sea of electrons model for the following metals? (a) Iron, (b) Vanadium, (c) Silver
One important physical property of metals is their malleability. How does the sea of electrons model account for this property?
The sea of electrons model is not generally used for quantitative predictions of properties. What factors are left out of this model that might prevent quantitative precision?
How does the sea of electrons model of metallic bonding explain why metals are good conductors of electricity?
What is the key difference between metallic bonding (in the sea of electrons model) and ionic bonding (as described in Chapter 7) that explains why metals conduct electricity and ionic solids do not?
Draw a depiction of the band structure of a metal. Label the valence band and conduction band.
In terms of band theory, what is the difference between a conductor and an insulator? Between a conductor and a semiconductor?
The conductivity of semiconductors increases as temperature is increased. Using band theory, explain this observation.
Use the web to find out what a “III–V” semiconductor is. How is this type of semiconductor related to silicon?
Explain how doping affects the electronic properties of a semiconductor.
What type of atom is needed as a dopant in an n-type semiconductor? Why is it called n-type?
What type of atom is needed as a dopant in a p-type semi conductor? Why is it called p-type?
Is an n-type semiconductor actually negatively charged?
How does a p-n junction serve as a voltage-gated switch?
Suppose that a device is using a 15.0-mg sample of silicon that is doped with 1 × 10-5 % (by mass) phosphorus. How many phosphorus atoms are in the sample?
What is an instantaneous dipole?
Why are dispersion forces attractive?
If a molecule is not very polarizable, how will it respond to an external electric field?
What is the relationship between polarizability and dispersion forces?
Under what circumstances are ion–dipole forces important?
What is the specific feature of N, O, and F that causes them to play a role in hydrogen bonding?
Identify the kinds of intermolecular forces (London dispersion, dipole–dipole, or hydrogen bonding) that are the most important in each of the following substances. (a) Methane (CH4), (b)
Rank the following in order of increasing strength of intermolecular forces in the pure substances.(a) CH3CH2CH2CH3 (butane), (b) CH3OH (methanol), (c) He
Describe how interactions between molecules affect the vapor pressure of a liquid.
What makes a chemical compound volatile?
Answer each of the following questions with increases, decreases, or does not change.(a) If the intermolecular forces in a liquid increase, the normal boiling point of the liquid — .(b) If the
Why must the vapor pressure of a substance be measured only after dynamic equilibrium is established?
Suppose that three unknown pure substances are liquids at room temperature. You determine that the boiling point of substance A is 538C, that of substance B is 1178C, and that of substance C is 778C.
Rank the following hydrocarbons in order of increasing vapor pressure: C2H6, C10H22, CH4, C7H16, C22H46.
Draw the meniscus of a fluid in a container where the interactions among the liquid molecules are weaker than those between the liquid and the container molecules.
When water is in a glass tube such as a buret, in which direction does the meniscus curve? What does this observation say about the relative magnitude of adhesion and cohesion in that system?
Why is temperature increased to start most addition polymerization reactions?
What is meant by the term chain termination in a polymerization reaction?
The monomer of polyvinylchloride is H2C ═ CHCl. Draw an example of an isotactic PVC polymer.
Why are isotactic or syndiotactic polymers often more attractive for materials development?
Nylon-6 is made from a single monomer: H₂N OH Sketch a section of the polymer chain in Nylon-6.
What are the products of a condensation polymerization reaction?
Distinguish between a block copolymer and a graft copolymer.
Use the web to look up the polymers used for six synthetic fibers. Classify the polymers as (a) Addition or condensation polymers and (b) As alternating, block or graft copolymers if they are
What is the key physical property that characterizes a thermoplastic polymer?
What conditions would prohibit the use of a thermoplastic polymer?
What happens molecularly in a thermosetting polymer when it is heated?
What structural characteristics are needed for additives such as plasticizers?
Use the web to find out what pencil erasers are made of. Would it be possible to form a new shape of an eraser by melting it and pouring it into a mold?
Use the web to find an application where the presence of isotactic, syndiotactic, or atactic polymers affects the physical properties important for an application of a polymer.
Define the terms substrate and mask in the context of microfabrication of MEMS devices.
Silicon nitride is a commonly used masking material in microfabrication. Based on the positions of silicon and nitrogen in the periodic table, what is the most likely chemical formula for silicon
Silicon dioxide is also used as a masking material in microfabrication. If a silicon substrate with an SiO2 mask is wet etched by HNO3/HF, one of the reactions that takes place will be between SiO2
In what way(s) are wet etching and plasma etching similar?
Estimate the number of atoms that would have to be removed from a silicon substrate to produce a rectangular channel 5 μm wide, 10 μm deep, and 20 μm long. (The density of silicon is 2.330 g cm-3.)
An important category of MEMS devices is micro-actuators. These devices produce mechanical motion in response to some electrical signal. Search the web for information and write a short paragraph
Using circles, draw regular two-dimensional arrangements that demonstrate low packing efficiency and high packing efficiency.
What is the difference between a bonding orbital and an antibonding orbital?
Describe how the combination of atomic orbitals gives rise to bands in the limit of large numbers of atoms.
Most gaseous compounds consist of small molecules, while polymers are never gaseous at room temperature. Explain this observation based on intermolecular forces.
Why are dipole–dipole forces typically stronger than dispersion forces?
Carbon tetrachloride (CCl4) is a liquid at room temperature and pressure, whereas ammonia (NH3) is a gas. How can these observations be rationalized in terms of intermolecular forces?
Explain from a molecular perspective why graphite has properties that are useful for lubrication.
A substance is observed to have a high surface tension. What predictions can you make about its vapor pressure and boiling point?
Suppose that three unknown pure substances are liquids at room temperature. You make vapor pressure measurements and find that substance Q has a pressure of 110 torr, substance R has a pressure of 42
If shown structures of monomers that might polymerize, what would you look for to determine if the type of polymerization would be addition?
Why is there no isotactic or syndiotactic form of polyethylene?
The following data show the vapor pressure of liquid propane as a function of temperature.(a) Plot a vapor pressure curve for propane and use it to estimate the normal boiling point. (b) Use your
Cylinders of compressed gas are equipped with pressure gauges that allow the user to monitor the amount of gas remaining. But such gauges are not useful for substances like propane or carbon dioxide,
Geckos are known for their ability to climb smooth vertical walls or windows. Recent research has shown that this unusual trait results from dispersion forces between the surface and the tips of tiny
If you place 1.0 L of ethanol (C2H5OH) in a room that is 3.0 m long, 2.5 m wide, and 2.5 m high, will all the alcohol evaporate? If some liquid remains, how much will there be? The vapor pressure of
An environmental engineering team is brought in to investigate a small oil spill caused by a leak in a crude oil pipeline. They find that the average molar mass of a sample collected from the spilled
Do a web search to find out how p- and n-type semiconductors can be used in designing solar panels. Write a short paragraph explaining what you learn. What new types of materials are being considered
Hydraulic fluids are liquids moving in a confined space under pressure, and they can serve many purposes in engineering designs. One use of hydraulic fluids is lubrication. Suppose you need to choose
It is possible to make syndiotactic polystyrene, although most polystyrene is atactic. Syndiotactic polystyrene melts at 2708C while atactic polystyrene melts closer to 2408C.(a) Why might this
A business manager wants to provide a wider range of p- and n-type semiconductors as a strategy to enhance sales. You are the lead materials engineer assigned to communicate with this manager. How
The doping of semiconductors can be done with enough precision to tune the size of the band gap in the material. Generally, in order to have a larger band gap, the dopant should be smaller than the
If you know the density of a material and the length of the edge of its cubic lattice, how would you determine if it is face-centered cubic, body-centered cubic, or simple cubic? Would you have to
If a pin is run across a magnet a number of times, it will become magnetized. How could this phenomenon be used as an analogy to describe polarization in atoms and molecules?
You go into the laboratory to look for a squirt bottle containing acetone. You find two unlabeled bottles with different colored tops suggesting they are different liquids. Unfortunately, you have a
A materials engineer, with an eye toward cost, wants to obtain a material whose degree of polymerization is high. What types of measurements must be made in the laboratory to determine whether the
How is polarizability related to the periodic trends of elements in the periodic table?
Cryolite (Na3AlF6) is used in refining aluminum. Use the web to look up what this addition does for the process, and relate it to the concepts of intermolecular forces from this chapter.
Use the web to look up the percentage of dopant for a commercially available p-type semiconductor. Imagine that you were setting up a process for doping 1 metric ton of silicon with this dopant. (a)
Use the web to look up the percentage of dopant for a commercially available n-type semiconductor. Imagine that you were setting up a process for doping 1 metric ton of silicon with this dopant. (a)
List reasons why there might be a connection between the amount of energy used by a country and its economic development.
Heating a 24.0-g aluminum can raises its temperature by 15.08C. Find the value of q for the can.Strategy Heat flow depends on the heat capacity of the material being heated, the size of the sample,
What differences (if any) would you expect to find between the energy use patterns of the United States shown in Figure 9.2 and Figure 9.3 and use in Figure 9.2Figure 9.3 (a) European countries
What are the advantages of electricity as a type of energy that make it worth generating despite the sizable losses that occur during this process?
The total energy supply for the United States in the year 2016, as shown in Figure 9.2, was 111.26 × 1015 Btu.Figure 9.2(a) What percentage of that energy was obtained from imports? (b) What
A calorimeter is to be used to compare the energy content of some fuels. In the calibration of the calorimeter, an electrical resistance heater supplies 100.0 J of heat and a temperature increase of
Using the value you calculate from part (a) in the previous problem and the fact that an average barrel of petroleum has an energy equivalent of 5.85 million Btu, how many barrels of oil, on average,
Distinguish between kinetic and potential energy.
Define the term internal energy.
What is the kinetic energy of a single molecule of oxygen if it is traveling at 1.5 × 103 m/s?
The kinetic energy of molecules is often used to induce chemical reactions. The bond energy in an O2 molecule is 8.22 × 10-19 j. Can an O2 molecule traveling at 780 m/s provide enough energy to
Analyze the units of the quantity (pressure 3 volume) and show that they are energy units, consistent with the idea of PV-work.
How many kilojoules are equal to 3.27 L atm of work?
Define the term hydrocarbon.
What are the products of the complete combustion of a hydrocarbon?
According to Figure 9.2, the total energy supply in the United States in 2016 was 111.26 × 1015 Btu. Express this value in joules and in calories.Figure 9.2 Coal 14.58/ NGL 4.74 Natural
Carry out the following conversions of energy units:(a) 14.3 Btu into calories, (b) 1.4 × 105 cal into joules,(c) 31.6 mJ into Btu
If a machine does 4.8 × 103 kJ of work after an input of 7.31 × 104 kJ of heat, what is the change in internal energy for the machine?

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