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engineering
the science and engineering of materials

The Science And Engineering Of Materials 7th Edition Donald R. Askeland, Wendelin J. Wright - Solutions

Enzymes are kinetically important for many of the complex reactions necessary for plant and animal life to exist. However, only a tiny amount of any particular enzyme is required for these complex reactions to occur. Explain.
Individuals who suffer from lactose intolerance do not produce enough of the enzyme lactase. Explain why this is an issue.
The combustion of carbohydrates and the combustion of fats are both exothermic processes, yet the combustion of carbohydrates is a faster process. How can this be?
A certain first-order reaction is 45.0% complete in 65s. What are the values of the rate constant and the half-life for this process?
A first-order reaction is 75.0% complete in 320. s.a. What are the first and second half-lives for this reaction? b. How long does it take for 90.0% completion?
A certain substance, initially present at 0.0800 M, decomposes by zero-order kinetics with a rate constant of 2.50 × 10-2 mol/L ? s. Calculate the time (in seconds) required for the system to reach a concentration of 0.0210 M.
The mechanism for the gas-phase reaction of nitrogen dioxide with carbon monoxide to form nitric oxide and carbon dioxide is thought to be Write the rate law expected for this mechanism. What is the overall balanced equation for the reaction? NO₂ + NO₂ NO3 + CO → NO3 + NO NO₂ +
One reason suggested for the instability of long chains of silicon atoms is that the decomposition involves the transition state shown below:The activation energy for such a process is 210 kJ/mol, which is less than either the Si-Si or the Si-H bond energy. Why would a similar mechanism not be
The rate constant for the gas-phase decomposition of N2O5,has the following temperature dependence: Make the appropriate graph using these data, and determine the activation energy for this reaction. N₂O, (g) 2NO₂(g) + O₂(g)
DDT (molar mass = 354.49 g/mol) was a widely used insecticide that was banned from use in the United States in 1973. This ban was brought about due to the persistence of DDT in many different ecosystems, leading to high accumulations of the substance in many birds of prey. The insecticide was shown
Theophylline is a pharmaceutical drug that is sometimes used to help with lung function. You observe a case where the initial lab results indicate that the concentration of theophylline in a patient’s body decreased from 2.0 × 10-3 M to 1.0 × 10-3 M in 24 hours. In another 12 hours the drug
Consider two reaction vessels, one containing A and the other containing B, with equal concentrations at t = 0. If both substances decompose by first-order kinetics, where how much time must pass to reach a condition such that [A] = 4.00[B]? KA KB = 4.50 x 10-4 S-1 3.70 X 10-3 S-1
Cobra venom helps the snake secure food by binding to acetylcholine receptors on the diaphragm of a bite victim, leading to the loss of function of the diaphragm muscle tissue and eventually death. In order to develop more potent antivenins, scientists have studied what happens to the toxin once it
A certain reaction has an activation energy of 54.0 kJ/mol. As the temperature is increased from 22οC to a higher temperature, the rate constant increases by a factor of 7.00. Calculate the higher temperature.
The thiosulfate ion (S2O32-) is oxidized by iodine as follows:In a certain experiment, 7.05 × 10-3 mol/L of S2O32- is consumed in the first 11.0 seconds of the reaction. Calculate the rate of consumption of S2O32-. Calculate the rate of production of iodide ion. 2S₂O3(aq) + 1₂(aq) S4O² (aq) +
Experiments have shown that the average frequency of chirping by a snowy tree cricket (Oecanthus fultoni) depends on temperature as shown in the table.What is the apparent activation energy of the process that controls the chirping? What is the rate of chirping expected at a temperature of 7.5οC?
Most reactions occur by a series of steps. The energy profile for a certain reaction that proceeds by a two-step mechanism is On the energy profile, indicate a. The positions of reactants and products.b. The activation energy for the overall reaction.c. ΔE for the reaction.d. Which point
Hydrogen peroxide and the iodide ion react in acidic solution as follows: The kinetics of this reaction were studied by following the decay of the concentration of H2O2 and constructing plots of ln[H2O2] versus time. All the plots were linear and all solutions had [H2O2]0 = 8.0 × 10-4 mol/L.
Consider an equilibrium mixture of four chemicals (A, B, C, and D, all gases) reacting in a closed flask according to the equation: a. You add more A to the flask. How does the concentration of each chemical compare to its original concentration after equilibrium is reestablished? Justify your
The boxes shown below represent a set of initial conditions for the reaction: Draw a quantitative molecular picture that shows what this system looks like after the reactants are mixed in one of the boxes and the system reaches equilibrium. Support your answer with calculations. K = 25
What is the law of mass action? Is it true that the value of K depends on the amounts of reactants and products mixed together initially? Explain. Is it true that reactions with large equilibrium constant values are very fast? Explain. There is only one value of the equilibrium constant for a
What is the difference between K and Kp? When does K = Kp for a reaction? When does K ≠ Kp for a reaction? If the coefficients in a reaction equation are tripled, how is the new value of K related to the initial value of K? If an equation for a reaction is reversed, how is the value of Kp for the
Explain why the development of a vapor pressure above a liquid in a closed container represents an equilibrium. What are the opposing processes? How do we recognize when the system has reached a state of equilibrium? Evaporation Condensation
Distinguish between the terms equilibrium constant and reaction quotient. When Q = K, what does this say about a reaction? When Q < K, what does this say about a reaction? When Q > K, what does this say about a reaction?
Consider the reaction A(g) + B(g) ⇌ C(g) + D(g) . A friend asks the following: “I know we have been told that if a mixture of A, B, C, and D is at equilibrium and more of A is added, more C and D will form. But how can more C and D form if we do not add more B?” What do you tell your friend?
A common type of reaction we will study is that having a very small K value (K << 1). Solving for equilibrium concentrations in an equilibrium problem usually requires many mathematical operations to be performed. However, the math involved when solving equilibrium problems for reactions
The reaction to prepare methanol from carbon monoxide and hydrogen is exothermic. If you wanted to use this reaction to produce methanol commercially, would high or low temperatures favor a maximum yield? Explain. CO(g) + H₂(g) → CH₂OH(g)
The value of the equilibrium constant K depends on which of the following (more than one answer may be correct)? a. The initial concentrations of the reactants.b. The initial concentrations of the products.c. The temperature of the system.d. The nature of the reactants and products. Explain.
The only “stress” (change) that also changes the value of K is a change in temperature. For an exothermic reaction, how does the equilibrium position change as temperature increases, and what happens to the value of K? Answer the same questions for an endothermic reaction. If the value of K
For the reaction it is determined that, at equilibrium at a particular temperature, the concentrations are as follows: [NO(g)] = 8.1 × 10-3 M, [H2(g)] = 4.1 × 10-5 M, [N2(g)] = 5.3 × 10-2 M, and [H2O(g)] = 2.9 × 10-3 M. Calculate the value of K for the reaction at this temperature. 2NO(g)
Consider the following reaction at 725°C: At equilibrium, a 4.50-L container has 2.6 g of carbon, CO2 at a partial pressure of 0.0020 atm, and a total pressure of 0.572 atm. Calculate Kp for this reaction at 725°C. C(s) + CO₂(g) → 2CO(g)
Suppose a reaction has the equilibrium constant K = 1.3 × 108 . What does the magnitude of this constant tell you about the relative concentrations of products and reactants that will be present once equilibrium is reached? Is this reaction likely to be a good source of the products?
Suppose a reaction has the equilibrium constant K = 1.7 × 10-8 at a particular temperature. Will there be a large or small amount of unreacted starting material present when this reaction reaches equilibrium? Is this reaction likely to be a good source of products at this temperature?
A 1.00-L flask was filled with 2.00 moles of gaseous SO2 and 2.00 moles of gaseous NO2 and heated. After equilibrium was reached, it was found that 1.30 moles of gaseous NO was present. Assume that the reactionoccurs under these conditions. Calculate the value of the equilibrium constant, K, for
Ethyl acetate is synthesized in a nonreacting solvent (not water) according to the following reaction:For the following mixtures (a–d), will the concentration of H2O increase, decrease, or remain the same as equilibrium is established?a. [CH3CO2C2H5] = 0.22 M, [H2O] = 0.10 M, [CH3CO2H] = 0.010 M,
For the reaction K = 2.4 × 10-3 at a given temperature. At equilibrium in a 2.0-L container it is found that [H2O(g)] = 1.1 × 10-1 M and [H2(g)] = 1.9 × 10-2 M. Calculate the moles of O2(g) present under these conditions. 2H₂O(g) = +2H₂(g) + O₂(g)
The creation of shells by mollusk species is a fascinating process. By utilizing the Ca2+ in their food and aqueous environment, as well as some complex equilibrium processes, a hard calcium carbonate shell can be produced. One important equilibrium reaction in this complex process isIf 0.16 mole
At 2200οC, Kp = 0.050 for the reactionWhat is the partial pressure of NO in equilibrium with N2 and O2 that were placed in a flask at initial pressures of 0.80 and 0.20 atm, respectively? N₂(g) + O₂(g)2NO(g)
At 35οC, K = 1.6 × 10-5 for the reactionCalculate the concentrations of all species at equilibrium for each of the following original mixtures. a. 2.0 moles of pure NOCl in a 2.0-L flaskb. 1.0 mole of NOCl and 1.0 mole of NO in a 1.0-L flaskc. 2.0 moles of NOCl and 1.0 mole of Cl2 in a 1.0-L
For the reaction Kp = 2.00 at some temperature. If this reaction at equilibrium has a total pressure of 6.00 atm, determine the partial pressures of CO2 and CO in the reaction container. C(s) + CO₂(g): 2CO(g)
Solid NH4HS decomposes by the following endothermic process:a. What effect will adding more NH3(g) have on the equilibrium?b. What effect will adding more NH4HS(s) have on the equilibrium?c. What effect will increasing the volume of the container have on the equilibrium?d. What effect will
Novelty devices for predicting rain contain cobalt(II) chloride and are based on the following equilibrium: What color will such an indicator be if rain is imminent? Pink Purple (S)09.100(8)0²H9 + (8)OH9 + (s)[Doე
Old-fashioned “smelling salts” consist of ammonium carbonate, (NH4)2CO3. The reaction for the decomposition of ammonium carbonateis endothermic. Would the smell of ammonia increase or decrease as the temperature is increased? (NH4)₂CO3(s)2NH3(g) + CO₂(g) + H₂O(g)
Suppose K = 4.5 × 10-3 at a certain temperature for the reactionIf it is found that the concentration of PCl5 is twice the concentration of PCl3, what must be the concentration of Cl2 under these conditions? PC15 (8) PC13 (8) PC13(g) + Cl₂(g)
At a certain temperature, K = 9.1 × 10-4 for the reactionCalculate the concentrations of Fe3+, SCN-, and FeSCN2+ in a solution that is initially 2.0 M FeSCN2+. 3+ FeSCN2+ (aq) Fe³+ (aq) + SCN- (aq)
For the following reaction at a certain temperature it is found that the equilibrium concentrations in a 5.00-L rigid container are [H2] = 0.0500 M, [F2] = 0.0100 M, and [HF] = 0.400 M. If 0.200 mole of F2 is added to this equilibrium mixture, calculate the concentrations of all gases once
Peptide decomposition is one of the key processes of digestion, where a peptide bond is broken into an acid group and an amine group. We can describe this reaction as follows:If we place 1.0 mole of peptide into 1.0 L water, what will be the equilibrium concentrations of all species in this
Methanol, a common laboratory solvent, poses a threat of blindness or death if consumed in sufficient amounts. Once in the body, the substance is oxidized to produce formaldehyde (embalming fluid) and eventually formic acid. Both of these substances are also toxic in varying levels. The equilibrium
At a particular temperature, 8.1 moles of NO2 gas are placed in a 3.0-L container. Over time the NO2 decomposes to NO and O2:At equilibrium the concentration of NO(g) was found to be 1.4 mol/L. Calculate the value of K for this reaction. 2NO₂(g) 2NO(g) + O₂(g)
A sample of solid ammonium chloride was placed in an evacuated chamber and then heated, causing it to decompose according to the following reaction:In a particular experiment, the equilibrium partial pressure of NH3(g) in the container was 2.9 atm. Calculate the value of Kp for the decomposition of
Many sugars undergo a process called mutarotation, in which the sugar molecules interconvert between two isomeric forms, finally reaching an equilibrium between them. This is true for the simple sugar glucose, C6H12O6, which exists in solution in isomeric forms called alpha-glucose and
In a given experiment, 5.2 moles of pure NOCl were placed in an otherwise empty 2.0-L container. Equilibrium was established by the following reaction:a. Using numerical values for the concentrations in the Initial row and expressions containing the variable x in both the Change and Equilibrium
For the following endothermic reaction at equilibrium: which of the following changes will increase the value of K? a. Increasing the temperatureb. Decreasing the temperaturec. Removing SO3(g) (constant T)d. Decreasing the volume (constant T)e. Adding Ne(g) (constant T)f. Adding SO2(g)
Consider the following exothermic reaction at equilibrium: Predict how the following changes affect the number of moles of each component of the system after equilibrium is reestablished by completing the table below. Complete the table with the terms increase, decrease, or no change.
At 5000 K and 1.000 atm, 83.00% of the oxygen molecules in a sample have dissociated to atomic oxygen. At what pressure will 95.0% of the molecules dissociate at this temperature?
For the reaction K = 400. at 35.0οC. If 2.00 moles each of NH3, H2S, and NH4HS are placed in a 5.00-L vessel, what mass of NH4HS will be present at equilibrium? What is the pressure of H2S at equilibrium? NH3(g) + H₂S(g) —NH4HS(s)
In a solution with carbon tetrachloride as the solvent, the compound VCl4 undergoes dimerization:When 6.6834 g VCl4 is dissolved in 100.0 g carbon tetrachloride, the freezing point is lowered by 5.97οC. Calculate the value of the equilibrium constant for the dimerization of VCl4 at this
The formation of glucose from water and carbon dioxide is an extremely important reaction for life to exist. Plants perform this reaction through the process of photosynthesis, creating the base of the food chain. The unbalanced reaction is At a particular temperature, the following
Find a time-temperature-transformation (TTT) diagram for 1340 steel. Assume that the steel is held at 1330 °F for 1 h, quenched to 800 °F and held for 1000 s at this temperature, and then cooled in air to room temperature.(a) What is the microstructure and hardness of the steel after the heat
What is the difference between cast iron and steels?
To what do the A1, A3, and Acm temperatures refer? Are these temperatures constant?
A manufacturing plant requires 15 lb of AISI 8620 per final product. The plant makes 700 units per day (three shifts) six days a week, 50 weeks a year. How many tons of yttrium is this plant consuming per year if nothing is wasted?
Calculate the amounts of ferrite, cementite, primary microconstituent, and pearlite in the following steels:(a) 1015;(b) 1035;(c) 1095; and(d) 10130.
What do the terms low-, medium-, and high-carbon steel mean?
Complete the following table: A₁ temperature A3 or Acm temperature Full annealing temperature Normalizing temperature Process annealing temperature Spheroidizing temperature 1035 Steel 10115 Steel
Two samples of steel contain 93% pearlite. Estimate the carbon content of each sample if one is known to be hypoeutectoid and the other hypereutectoid.
Explain the following heat treatments: (a) Process anneal; (b) Austenitizing;(c) Annealing; (d) Normalizing; and (e) Quenching.
Define austempering and explain its purpose.
Explain why, strictly speaking, TTT diagrams can be used for isothermal treatments only.
Define ausforming and explain its purpose.
Explain the difference between hardenability and hardness. Explain using a sketch how hardenability of steels is measured.
Water hardenable 1095 steel is supposed to be tempered at 500°C, but a negligent operator does not check the automatic process control and so it is tempered at 450°C. What is the hardness of the asproduced steel compared to the specified steel?
You encounter a specification that lists a Jominy distance of 1.27 cm and a bar diameter of 3.81 cm. What is the H coefficient for this?
What are tool steels?
What is the principle of the surface hardening of steels using carburizing and nitriding?
Why is it that the strength of the heataffected zone is higher for low-carbon steels? What is the role of retained austenite in this case?
Why is it easy to weld low-carbon steels, but difficult to weld high-carbon steels?
We would like to produce a 2-in.-thick steel wear plate for a rock-crushing unit. To avoid frequent replacement of the wear plate, the hardness should exceed HRC 38 within 0.25 in. of the steel surface. The center of the plate should have a hardness of no more than HRC 32 to ensure some toughness.
What is a stainless steel? Why are stainless steels stainless?
Surplus stock inventory contains 15 ton 304, 5.2 ton 304L, 1 ton 316, and 4.7 ton 440C stainless steel. A spike in molybdenum prices makes it worthwhile to sell the steels that contain it. How much molybdenum is contained in each of the steels and how much total mass is being sold?
A food processing plant that is designed to use 5.75 metric tons of 316 stainless steel will actually use 115% of the design specification. How many moles of chromium must be refined for this? Assume the refinery loses 5% of what it refines.
Define cast iron using the Fe-Fe3C phase diagram.
What are the different types of cast irons? Explain using a sketch.
How much would 50 kg of the hypothetical alloy 5074-O cost in raw material prices using the estimates given in Table 14-1? Table 14-1 Specific strength and cost of nonferrous alloys, steels, and polymer
You would like to produce a gray iron casting that freezes with no primary austenite or graphite. If the carbon content in the iron is 3.5%, what percentage of silicon must you add?
A quenched and tempered 10110 steel is found to have surface cracks that cause the heat-treated part to be rejected by the customer. Why did the cracks form? Design a heat treatment, including appropriate temperatures and times, to minimize these problems.
Design a corrosion-resistant steel to use for a pump that transports liquid helium at 4 K in a superconducting magnet.
Design a heat treatment for a hook made from a 1-in.-diameter steel rod having a microstructure containing a mixture of ferrite, bainite, and martensite after quenching. Estimate the mechanical properties of your hook.
Design an annealing treatment for a 1050 steel. Be sure to include details of temperatures, cooling rates, microstructures, and properties.
We say that copper can contain up to 40% Zn or 9% Al and still be single phase.How do we explain this statement in view of the phase diagram for the Cu-Zn system? Temperature (°C) 1100 1000 900 800 700 600 500 400 300 α В B L Y E 0 200 100 0 Cu 10 20 30 40 50 60 70 80 90 Zn Weight percent
Design a process to produce a 0.5-cmdiameter steel shaft having excellent toughness as well as excellent wear and fatigue resistance. The surface hardness should be at least HRC 60, and the hardness 0.01 cm beneath the surface should be approximately HRC 50. Describe the process, including details
Would you expect a 2024-T9 aluminum alloy to be stronger or weaker than a 2024-T6 alloy? Explain.
A Ti-Mn alloy is composed of 20 wt% manganese and is kept at 550°C. What phase(s) are present? See Figure 14-8(d). Temperature (°C) 1200 1000 800 600 400 200 Ti В α ‚a + ß 5 10 15 Weight percent tin (a) 20 Temperature (°C) 1200 1100 1000 900 800 700 Ti В 8 a+ß- α + Ti3Al 02
A 5182-O aluminum alloy part that had been exposed to salt water showed severe corrosion along the grain boundaries. Explain this observation based on the expected phases at room temperature in this alloy.
Based on the photomicrograph in Figure 14-7(a), would you expect the γ' precipitate or the carbides to provide a greater strengthening effect in superalloys at low temperatures? Explain. (a) TAS
What temperature ranges correspond to the phases of Cu-Sn alloys?(a) η at 60 wt% Sn;(b) ζ at 34 wt% Sn;(c) γ at 30 wt% Sn; and(d) α at 0 wt% Sn.
A number of casting alloys have very high lead contents; however, the Pb content in wrought alloys is comparatively low. Why isn’t more lead added to the wrought alloys? What precautions must be taken when a leaded wrought alloy is hot worked or heat treated?
Hastelloy is used for chemical reactors, pipes, and other vessels that contain highvalue, highly corrosive materials. Hastelloy is mostly nickel. How much more load can Hastelloy B-2 sustain compared to pure, cold-worked nickel?
What is a refractory metal or refractory alloy? What is a precious metal?
For what applications are Pt, Rh, Pd, and Ag used?

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