What are the distinguishing features of each extraction process: pyrometallurgy

Hydrogen is by far the most abundant element cosmically. In interstellar space, it exists mainly as H2. In contrast, on Earth, it exists very rarely as H2 and is ninth in abundance in the crust. Why is hydrogen so abundant in the universe? Why is hydrogen so rare as a diatomic gas in Earths atmosphere?

Metallic elements can be recovered from ores that are oxides, carbonates, halides, or sulfides. Give an example of each type.

The location of elements in the regions of Earth has enormous practical importance. (a) Define differentiation, and explain which physical property of a substance is primarily responsible for this process. (b) What are the four most abundant elements in the crust? (c) Which element is abundant in the crust and mantle but not the core?

How does the position of a metal in the periodic table relate to whether it occurs primarily as an oxide or as a sulfide?

What material is the source for commercial production of each of the following elements: (a) aluminum; (b) nitrogen; (c) chlorine; (d) calcium; (e) sodium?

Aluminum is widely distributed throughout the world in the form of aluminosilicates. What property of these minerals prevents them from being a source of aluminum?

Describe two ways in which the biosphere has influenced the composition of Earths crust.

Use atomic and molecular properties to explain why life is based on carbon rather than some other element, such as silicon.

Define fixation. Name two elements that undergo environmental fixation. What natural forms of them are fixed?

Carbon dioxide enters the atmosphere by natural processes and from human activity. Why is the latter a cause of concern?

Diagrams of environmental cycles are simplified to omit minor contributors. For example, the production of lime from limestone is not shown in the cycle for carbon (Figure 22.5, p. 983). Which labeled category in the figure includes this process? Name two other processes that contribute to this category.

Describe three pathways for the utilization of atmospheric nitrogen. Is human activity a significant factor? Explain.

Why dont the N-containing species in Figure 22.6 (p. 984) include rings or long chains with NN bonds?

(a) Which region of Earths crust is not involved in the phosphorus cycle? (b) Name two roles organisms play in the cycle.

Nitrogen fixation requires a great deal of energy because the N2 bond is strong. (a) How do the processes of atmospheric and industrial fixation reflect this energy requirement? (b) How do the thermodynamics of the two processes differ? (Hint: Examine the respective heats of formation.) (c) In view of the mild conditions for biological fixation, what must be the source of the great deal of energy? (d) What would be the most obvious environmental result of a low activation energy for N2 fixation?

The following steps are unbalanced half-reactions involved in the nitrogen cycle. Balance each half-reaction to show the number of electrons lost or gained, and state whether it is an oxidation or a reduction (all occur in acidic conditions): (a) N2(g) - NO(g) (b) N2O(g) - NO2(g) (c) NH3(aq) - NO2 2(aq) (d) NO3 2(aq) - NO2 2(aq) (e) N2(g) - NO3 2(aq)

The use of silica to form slag in the production of phosphorus from phosphate rock was introduced by Robert Boyle more than 300 years ago. When fluorapatite [Ca5(PO4)3F] is used in phosphorus production, most of the fluorine atoms appear in the slag, but some end up in the toxic and corrosive gas SiF4. (a) If 15% by mass of the fluorine in 100. kg of Ca5(PO4)3F forms SiF4, what volume of this gas is collected at 1.00 atm and the industrial furnace temperature of 1450.8C? (b) In some facilities, the SiF4 is used to produce sodium hexafluorosilicate (Na2SiF6) which is sold for water fluoridation: 2SiF4(g) 1 Na2CO3(s) 1 H2O(l) - Na2SiF6(aq) 1 SiO2(s) 1 CO2(g) 1 2HF(aq) How many cubic meters of drinking water can be fluoridated to a level of 1.0 ppm of F2 using the SiF4 produced in part (a)?

An impurity sometimes found in Ca3(PO4)2 is Fe2O3, which is removed during the production of phosphorus as ferrophosphorus (Fe2P). (a) Why is this impurity troubling from an economic standpoint? (b) If 50. metric tons of crude Ca3(PO4)2 contains 2.0% Fe2O3 by mass and the overall yield of phosphorus is 90.%, how many metric tons of P4 can be isolated?

Define: (a) ore; (b) mineral; (c) gangue; (d) brine.

Define: (a) roasting; (b) smelting; (c) flotation; (d) refining.

What factors determine which reducing agent is selected for producing a specific metal?

Use atomic properties to explain the reduction of a less active metal by a more active one: (a) in aqueous solution; (b) in the molten state. Give a specific example of each process.

What class of element is obtained by oxidation of a mineral? What class of element is obtained by reduction of a mineral?

Which set of elements gives each of the following alloys: (a) brass; (b) stainless steel; (c) bronze; (d) sterling silver? 1. Cu, Ag 2. Cu, Sn, Zn 3. Ag, Au 4. Fe, Cr, Ni 5. Fe, V 6. Cu, Zn

How are each of the following involved in iron metallurgy: (a) slag; (b) pig iron; (c) steel; (d) basic-oxygen process?

What are the distinguishing features of each extraction process: pyrometallurgy, electrometallurgy, and hydrometallurgy? Explain briefly how the types of metallurgy are used in the production of (a) Fe; (b) Na; (c) Au; (d) Al.

What property allows copper to be purified in the presence of iron and nickel impurities? Explain.

Why is cryolite used in the electrolysis of aluminum oxide?

(a) What is a kinetic isotope effect? (b) Do compounds of hydrogen exhibit a relatively large or small kinetic isotope effect? Explain. (c) Carbon compounds also exhibit a kinetic isotope effect. How do you expect it to compare in magnitude with that for hydrogen compounds? Why?

How is Le Chteliers principle involved in the production of elemental potassium?

Elemental Li and Na are prepared by electrolysis of a molten salt, whereas K, Rb, and Cs are prepared by chemical reduction. (a) In general terms, explain why the alkali metals cannot be prepared by electrolysis of their aqueous salt solutions. (b) Use ionization energies (see the Family Portraits, pp. 575 and 578) to explain why calcium should not be able to isolate Rb from molten RbX (X 5 halide). (c) Use physical properties to explain why calcium is used to isolate Rb from molten RbX. (d) Can Ca be used to isolate Cs from molten CsX? Explain.

A Downs cell operating at 77.0 A produces 31.0 kg of Na. (a) What volume of Cl2(g) is produced at 1.0 atm and 540.8C? (b) How many coulombs were passed through the cell? (c) How long did the cell operate?

(a) In the industrial production of iron, what is the reducing substance loaded into the blast furnace? (b) In addition to furnishing the reducing power, what other function does this substance serve? (c) What is the formula of the active reducing agent in the process? (d) Write equations for the stepwise reduction of Fe2O3 to iron in the furnace.

One of the substances loaded into a blast furnace is limestone, which produces lime in the furnace. (a) Give the chemical equation for the reaction forming lime. (b) Explain the purpose of lime in the furnace. The term flux is often used as a label for a substance acting as the lime does. What is the derivation of this word, and how does it relate to the function of the lime? (c) Write a chemical equation describing the action of lime flux.

The last step in the Dow process for the production of magnesium metal involves electrolysis of molten MgCl2. (a) Why isnt the electrolysis carried out with aqueous MgCl2? What are the products of this aqueous electrolysis? (b) Do the high temperatures required to melt MgCl2 favor products or reactants? (Hint: Consider the DH8 f of MgCl2.)

Iodine is the only halogen that occurs in a positive oxidation state, in NaIO3 impurities within Chile saltpeter, NaNO3. (a) Is this mode of occurrence consistent with iodines location in the periodic table? Explain. (b) In the production of I2, IO3 2 reacts with HSO3 2: IO3 2(aq) 1 HSO3 2(aq) - HSO4 2(aq) 1 SO4 22(aq) 1 H2O(l) 1 I2(s) [unbalanced] Identify the oxidizing and reducing agents. (c) If 0.78 mol % of an NaNO3 deposit is NaIO3, how much I2 (in g) can be obtained from 1.000 ton (2000. lb) of the deposit?

Selenium is prepared by the reaction of H2SeO3 with gaseous SO2. (a) What redox process does the sulfur dioxide undergo? What is the oxidation state of sulfur in the product? (b) Given that the reaction occurs in acidic aqueous solution, what is the formula of the sulfur-containing species? (c) Write the balanced redox equation for the process.

F2 and Cl2 are produced by electrolytic oxidation, whereas Br2 and I2 are produced by chemical oxidation of the halide ions in a concentrated aqueous solution (brine) by a more electronegative halogen. Give two reasons why Cl2 isnt prepared this way.

Silicon is prepared by the reduction of K2SiF6 with Al. Write the equation for this reaction. (Hint: Can F2 be oxidized in this reaction? Can K1 be reduced?)

What is the mass percent of iron in each of the following iron ores: Fe2O3, Fe3O4, FeS2?

Phosphorus is one of the impurities present in pig iron that is removed in the basic-oxygen process. Assuming that phosphorus is present as P atoms, write equations for its oxidation and subsequent reaction in the basic slag.

The final step in the smelting of FeCuS2 is Cu2S(s) 1 2Cu2O(s) - 6Cu(l) 1 SO2(g) (a) Give the oxidation states of copper in Cu2S, Cu2O, and Cu. (b) What are the oxidizing and reducing agents in this reaction?

Use equations to show how acid-base properties are used to separate Fe2O3 and TiO2 from Al2O3 in the Bayer process.

A piece of Al with a surface area of 2.5 m2 is anodized to produce a film of Al2O3 that is 23 mm (2331026 m) thick. (a) How many coulombs flow through the cell in this process (assume that the density of the Al2O3 layer is 3.97 g/cm3)? (b) If it takes 18 min to produce this film, what current must flow through the cell?

The production of H2 gas by the electrolysis of water typically requires about 400 kJ of energy per mole. (a) Use the relationship between work and cell potential (Section 21.4) to calculate the minimum work needed to form 1.0 mol of H2 gas at a cell potential of 1.24 V. (b) What is the energy efficiency of the cell operation? (c) Find the cost of producing 500. mol of H2 if electricity is $0.06 per kilowatt-hour (1 watt-second 5 1 joule).

(a) What are the components of the reaction mixture following the water-gas shift reaction? (b) Explain how zeolites are used to purify the H2 formed.

Metal sulfides are often first converted to oxides by roasting in air and then reduced with carbon to produce the metal. Why arent the metal sulfides reduced directly by carbon to yield CS2? Give a thermodynamic analysis of both processes for ZnS.

Explain in detail why a catalyst is used to produce SO3.

Among the exothermic steps in the manufacture of sulfuric acid is the process of hydrating SO3. (a) Write two chemical reactions that show this process. (b) Why is the direct reaction of SO3 with water not feasible?

Why is commercial H2SO4 so inexpensive?

(a) What are the three commercial products formed in the chlor-alkali process? (b) State an advantage and a disadvantage of the mercury-cell method for this process.

Consider the reaction of SO2 to form SO3 at standard conditions. (a) Calculate DG8 at 258C. Is the reaction spontaneous? (b) Why is the reaction not performed at 258C? (c) Is the reaction spontaneous at 500.8C? (Assume that DH8 and DS8 are constant with changing T.) (d) Compare K at 500.8C and at 258C. (e) What is the highest T at which the reaction is spontaneous?

If a chlor-alkali cell used a current of 33104 A, how many pounds of Cl2 would be produced in a typical 8-h operating day?

The products of the chlor-alkali process, Cl2 and NaOH, are kept separated. (a) Why is this necessary when Cl2 is the desired product? (b) ClO2 or ClO3 2 may form by disproportionation of Cl2 in basic solution. What determines which product forms? (c) What mole ratio of Cl2 to OH2 will produce ClO2? ClO3 2?

The key step in the manufacture of sulfuric acid is the oxidation of sulfur dioxide in the presence of a catalyst, such as V2O5. At 7278C, 0.010 mol of SO2 is injected into an empty 2.00-L container (Kp 5 3.18). (a) What is the equilibrium pressure of O2 that is needed to maintain a 1/1 mole ratio of SO3 to SO2? (b) What is the equilibrium pressure of O2 needed to maintain a 95/5 mole ratio of SO3 to SO2?

Tetraphosphorus decoxide (P4O10) is made from phosphate rock and used as a drying agent in the laboratory. (a) Write a balanced equation for its reaction with water. (b) What is the pH of a solution formed from the addition of 8.5 g of P4O10 in sufficient water to form 0.750 L? (See Table 18.5, p. 797, for additional information.)

Heavy water (D2O) is used to make deuterated chemicals. (a) What major species, aside from the starting compounds, do you expect to find in a solution of CH3OH and D2O? (b) Write equations to explain how these various species arise. (Hint: Consider the autoionization of both components.)

A blast furnace uses Fe2O3 to produce 8400. t of Fe per day. (a) What mass of CO2 is produced each day? (b) Compare this amount of CO2 with that produced by 1.0 million automobiles, each burning 5.0 gal of gasoline a day. Assume that gasoline has the formula C8H18 and a density of 0.74 g/mL, and that it burns completely. (Note that U.S. gasoline consumption is over 43108 gal/day.)

A major use of Cl2 is in the manufacture of vinyl chloride, the monomer of poly(vinyl chloride). The two-step sequence for formation of vinyl chloride is depicted below. 1 2 (a) Write a balanced equation for each step. (b) Write the overall equation. (c) What type of organic reaction is shown in step 1? (d) What type of organic reaction is shown in step 2? (e) If each molecule depicted in the initial reaction mixture represents 0.15 mol of substance, what mass (in g) of vinyl chloride forms?

In the production of magnesium, Mg(OH)2 is precipitated by using Ca(OH)2, which itself is insoluble. (a) Use Ksp values to show that Mg(OH)2 can be precipitated from seawater in which [Mg21] is initially 0.052 M. (b) If the seawater is saturated with Ca(OH)2, what fraction of the Mg21 is precipitated?

Step 1 of the Ostwald process for nitric acid production is 4NH3(g) 1 5O2(g) ------ Pt/Rh catalyst 4NO(g) 1 6H2O(g) An unwanted side reaction for this step is 4NH3(g) 1 3O2(g) - 2N2(g) 1 6H2O(g) (a) Calculate Kp for these two NH3 oxidations at 258C. (b) Calculate Kp for these two NH3 oxidations at 900.8C. (c) The Pt/Rh catalyst is one of the most efficient in the chemical industry, achieving 96% yield in 1 millisecond of contact with the reactants. However, at normal operating conditions (5 atm and 8508C), about 175 mg of Pt is lost per metric ton (t) of HNO3 produced. If the annual U.S. production of HNO3 is 1.013107 t and the market price of Pt is $1557/troy oz, what is the annual cost of the lost Pt (1 kg 5 32.15 troy oz)? (d) Because of the high price of Pt, a filtering unit composed of ceramic fiber is often installed, which recovers as much as 75% of the lost Pt. What is the value of the Pt captured by a recovery unit with 72% efficiency?

Several transition metals are prepared by reduction of the metal halide with magnesium. Titanium is prepared by the Kroll method, in which ore (ilmenite) is converted to the gaseous chloride, which is then reduced to Ti metal by molten Mg (see p. 1003). Assuming yields of 84% for step 1 and 93% for step 2, and an excess of the other reactants, what mass of Ti metal can be prepared from 21.5 metric tons of ilmenite?

The production of S8 from the H2S(g) found in natural gas deposits occurs through the Claus process (Section 22.5): (a) Use these two unbalanced steps to write an overall balanced equation for this process: (1) H2S(g) 1 O2(g) - S8(g) 1 SO2(g) 1 H2O(g) (2) H2S(g) 1 SO2(g) - S8(g) 1 H2O(g) (b) Write the overall reaction with Cl2 as the oxidizing agent instead of O2. Use thermodynamic data to show whether Cl2(g) can be used to oxidize H2S(g). (c) Why is oxidation by O2 preferred to oxidation by Cl2?

Acid mine drainage (AMD) occurs when geologic deposits containing pyrite (FeS2) are exposed to oxygen and moisture. AMD is generated in a multistep process catalyzed by acidophilic (acid-loving) bacteria. Balance each step and identify those that increase acidity: (1) FeS2(s) 1 O2(g) - Fe21(aq) 1 SO4 22(aq) (2) Fe21(aq) 1 O2(g) - Fe31(aq) 1 H2O(l) (3) Fe31(aq) 1 H2O(l) - Fe(OH)3(s) 1 H1(aq) (4) FeS2(s) 1 Fe31(aq) - Fe21(aq) 1 SO4 22(aq)

Below 9128C, pure iron crystallizes in a body-centered cubic structure (ferrite) with d 5 7.86 g/cm3; from 9128C to 13948C, it adopts a face-centered cubic structure (austenite) with d 5 7.40 g/cm3. Both types of iron form interstitial alloys with carbon. The maximum amount of carbon is 0.0218 mass % in ferrite and 2.08 mass % in austenite. Calculate the density of each alloy.

Why isnt nitric acid produced by oxidizing N2 as follows? (1) N2(g) 1 2O2(g) - 2NO2(g) (2) 3NO2(g) 1 H2O(l) - 2HNO3(aq) 1 NO(g) (3) 2NO(g) 1 O2(g) - 2NO2(g) 3N2(g) 1 6O2(g) 1 2H2O(l) - 4HNO3(aq) 1 2NO(g) (Hint: Evaluate the thermodynamics of each step.)

Before the development of the Downs cell, the Castner cell was used for the industrial production of Na metal. The Castner cell was based on the electrolysis of molten NaOH. (a) Write balanced cathode and anode half-reactions for this cell. (b) A major problem with this cell was that the water produced at one electrode diffused to the other and reacted with the Na. If all the water produced reacted with Na, what would be the maximum efficiency of the Castner cell expressed as moles of Na produced per mole of electrons flowing through the cell?

When gold ores are leached with CN2 solutions, gold forms a complex ion, Au(CN)2 2. (a) Find Ecell for the oxidation in air (PO2 5 0.21) of Au to Au1 in basic (pH 13.55) solution with [Au1] 5 0.50 M. Is the reaction Au1(aq) 1 e2 - Au(s), E8 5 1.68 V, spontaneous? (b) How does formation of the complex ion change E8 so that the oxidation can be accomplished?

Nitric oxide occurs in the tropospheric nitrogen cycle, but it destroys ozone in the stratosphere. (a) Write equations for its reaction with ozone and for the reverse reaction. (b) Given that the forward and reverse steps are first order in each component, write general rate laws for them. (c) Calculate DG8 for this reaction at 280. K, the average temperature in the stratosphere. (Assume that the DH8 and S8 values in Appendix B do not change with temperature.) (d) What ratio of rate constants is consistent with K at this temperature?

A key part of the carbon cycle is the fixation of CO2 by photosynthesis to produce carbohydrates and oxygen gas. (a) Using the formula (CH2O)n to represent a carbohydrate, write a balanced equation for the photosynthetic reaction. (b) If a tree fixes 48 g of CO2 per day, what volume of O2 gas measured at 1.0 atm and 788F does the tree produce per day? (c) What volume of air (0.040 mol % CO2) at the same conditions contains this amount of CO2?

Farmers use ammonium sulfate as a fertilizer. In the soil, nitrifying bacteria oxidize NH4 1 to NO3 2, a groundwater contaminant that causes methemoglobinemia (blue baby syndrome). The World Health Organization standard for maximum [NO3 2] in groundwater is 45 mg/L. A farmer adds 210. kg of (NH4)2SO4 to a field and 37% is oxidized to NO3 2. What is the groundwater [NO3 2] (in mg/L) if 1000. m3 of the water is contaminated?

The key reaction (unbalanced) in the manufacture of synthetic cryolite for aluminum electrolysis is HF(g) 1 Al(OH)3(s) 1 NaOH(aq) - Na3AlF6(aq) 1 H2O(l) Assuming a 95.6% yield of dried, crystallized product, what mass (in kg) of cryolite can be obtained from the reaction of 365 kg of Al(OH)3, 1.20 m3 of 50.0% by mass aqueous NaOH (d 5 1.53 g/mL), and 265 m3 of gaseous HF at 305 kPa and 91.58C? (Assume that the ideal gas law holds.)

Because of their different molar masses, H2 and D2 effuse at different rates (Section 5.5). (a) If it takes 16.5 min for 0.10 mol of H2 to effuse, how long does it take for 0.10 mol of D2 to do so in the same apparatus at the same T and P? (b) How many effusion steps does it take to separate an equimolar mixture of D2 and H2 to 99 mol % purity?

The disproportionation of CO to graphite and CO2 is thermodynamically favored but slow. (a) What does this mean in terms of the magnitudes of the equilibrium constant (K), rate constant (k), and activation energy (Ea)? (b) Write a balanced equation for the disproportionation of CO. (c) Calculate Kc at 298 K. (d) Calculate Kp at 298 K.

The overall cell reaction for aluminum production is 2Al2O3(in Na3AlF6) 1 3C(graphite) - 4Al(l) 1 3CO2(g) (a) Assuming 100% efficiency, how many metric tons (t) of Al2O3 are consumed per metric ton of Al produced? (b) Assuming 100% efficiency, how many metric tons of the graphite anode are consumed per metric ton of Al produced? (c) Actual conditions in an aluminum plant require 1.89 t of Al2O3 and 0.45 t of graphite per metric ton of Al. What is the percent yield of Al with respect to Al2O3? (d) What is the percent yield of Al with respect to graphite? (e) What volume of CO2 (in m3) is produced per metric ton of Al at operating conditions of 960.8C and exactly 1 atm?

World production of chromite (FeCr2O4), the main ore of chromium, was 1.973107 metric tons in 2006. To isolate chromium, a mixture of chromite and sodium carbonate is heated in air to form sodium chromate, iron(III) oxide, and carbon dioxide. The sodium chromate is dissolved in water, and this solution is acidified with sulfuric acid to produce the less soluble sodium dichromate. The sodium dichromate is filtered out and reduced with carbon to produce chromium(III) oxide, sodium carbonate, and carbon monoxide. The chromium(III) oxide is then reduced to chromium with aluminum metal. (a) Write balanced equations for each step. (b) What mass of chromium (in kg) could be prepared from the 2006 world production of chromite?

Like heavy water (D2O), so-called semi-heavy water (HDO) undergoes H/D exchange. The molecular scenes depict an initial mixture of HDO and H2 reaching equlibrium. O H D (a) Write the balanced equation for the reaction. (b) Is the value of K greater or less than 1? (c) If each molecule depicted represents 0.10 M, calculate K.

Even though most metal sulfides are sparingly soluble in water, their solubilities differ by several orders of magnitude. This difference is sometimes used to separate the metals by controlling the pH. Use the following data to find the pH at which you can separate 0.10 M Cu21 and 0.10 M Ni21: Saturated H2S 5 0.10 M Ka1 of H2S 5 931028 Ka2 of H2S 5 1310217 Ksp of NiS 5 1.1310218 Ksp of CuS 5 8310234

Ores with as little as 0.25% by mass of copper are used as sources of the metal. (a) How many kilograms of such an ore would be needed to construct another Statue of Liberty, which contains 2.03105 lb of copper? (b) If the mineral in the ore is chalcopyrite (FeCuS2), what is the mass % of chalcopyrite in the ore?

How does acid rain affect the leaching of phosphate into groundwater from terrestrial phosphate rock? Calculate the solubility of Ca3(PO4)2 in each of the following: (a) Pure water, pH 7.0 (Assume that PO4 32 does not react with water.) (b) Moderately acidic rainwater, pH 4.5 (Hint: Assume that all the phosphate exists in the form that predominates at this pH.)

The lead(IV) oxide used in car batteries is prepared by coating the electrode plate with PbO and then oxidizing it to lead dioxide (PbO2). Despite its name, PbO2 has a nonstoichiometric mole ratio of lead to oxygen of about 1/1.98. In fact, the holes in the PbO2 crystal structure due to missing O atoms are responsible for the oxides conductivity. (a) What is the mole % of O missing from the PbO2 structure? (b) What is the molar mass of the nonstoichiometric compound?

Chemosynthetic bacteria reduce CO2 by splitting H2S(g) instead of the H2O(g) used by photosynthetic organisms. Compare the free energy change for splitting H2S with that for splitting H2O. Is there an advantage to using H2S instead of H2O?

Silver has a face-centered cubic structure with a unit cell edge length of 408.6 pm. Sterling silver is a substitutional alloy that contains 7.5% copper atoms. Assuming the unit cell remains the same, find the density of silver and of sterling silver.

Earths mass is estimated to be 5.9831024 kg, and titanium represents 0.05% by mass of this total. (a) How many moles of Ti are present? (b) If half of the Ti is found as ilmenite (FeTiO3), what mass of ilmenite is present? (c) If the airline and auto industries use 1.003105 tons of Ti per year, how many years will it take to use up all the Ti (1 ton 5 2000 lb)?

In 1790, Nicolas Leblanc found a way to form Na2CO3 from NaCl. His process, now obsolete, consisted of three steps: 2NaCl(s) 1 H2SO4 (aq) - Na2SO4(aq) 1 2HCl(g) Na2SO4(s) 1 2C(s) - Na2S(s) 1 2CO2(g) Na2S(s) 1 CaCO3(s) - Na2CO3(s) 1 CaS(s) (a) Write a balanced overall equation for the process. (b) Calculate the DH8 f of CaS if DH8 rxn is 351.8 kJ/mol. (c) Is the overall process spontaneous at standard-state conditions and 298 K? (d) How many grams of Na2CO3 form from 250. g of NaCl if the process is 73% efficient?

Limestone (CaCO3) is the second most abundant mineral on Earth after SiO2. For many uses, it is first decomposed thermally to quicklime (CaO). MgO is prepared similarly from MgCO3. (a) At what T is each decomposition spontaneous? (b) Quicklime reacts with SiO2 to form a slag (CaSiO3), a byproduct of steelmaking. In 2010, the total steelmaking capacity of the U.S. steel industry was 2,236,000 tons per week, but only 84% of this capacity was utilized. If 50. kg of slag is produced per ton of steel, what mass (in kg) of limestone was used to make slag in 2010?