 Chemical reactions and physical processes on a large scale to convert raw materials into useful products.  Conditions of the reactions are controlled to produce the best yield of product possible at an economic rate. YIELD: Quantity of product formed  Theoretical: Predicted by equation  Actual: Quantity actually obtained 1

 Process to produce ammonia.  Developed by German Chemist Fritz Haber  N 2(g) + 3H 2(g)  2NH 3(g)  H = –46kJmol -1 CONDITIONS FOR HIGH YIELD  High pressure (less molecules on the product side)  Low temperature (forward reaction is exothermic) 2

ACTUAL CONDITIONS  High Pressure ( atmospheres pressure). If pressure is too high, expensive structural requirements are needed for the plant.  Moderately high temperature (~ 400 o C). If the temperature is low then the yield is high, but it takes a long time for the reaction to produce the product (Rate low) 3

 Iron catalyst increases rate of forward and back reaction.  Yield of ammonia is approximately 45% of the theoretical yield 4

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 Product of sulfur dioxide from sulfur or metal sulfides  S (s) + O 2(g)  SO 2(g)  2ZnS (s) + O 2(g)  2ZnO (s) +SO 2(g)  Conversion of sulfur dioxide to sulfur trioxide  2SO 2(g) + O 2(g)  2SO 3(g)  H = –99kJmol -1 6

 Absorption of sulfur trioxide into concentrated sulfuric acid to form oleum  SO 3(g) + H 2 SO 4(l)  H 2 S 2 O 7(l) REACTION THAT CONTROLS YIELD  2SO 2(g) + O 2(g)  2SO 3(g)  H = –99kJmol -1 CONDITIONS FOR HIGH YIELD  High pressure  Low temperature 7

ACTUAL CONDITIONS  Atmospheric pressure. Yield is about 85-90% at this pressure. Costs to increase pressure are not offset by much greater yield.  Temperature: 450 o C. Compromise between yield and rate.  Vanadium pentoxide catalyst (V 2 O 5 ) increases rate of reaction. 8

 Sulfur trioxide is dissolved in concentrated sulfuric acid as it forms to maximise yield.  Acid is transported as oleum (less corrosive) and diluted as required by buyer which reduces transport costs. H 2 S 2 O 7(l) + H 2 O (l)  2H 2 SO 4(aq)  600kJ of energy is released for every mole of acid formed. Some of this energy is used to produce electricity for the plant. 9

 Used to represent the movement of materials through various components of the plant.  May include diagrams of equipment or show the process through a series of boxes and arrows. May show quantities of material and energy. 10

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RAW MATERIALS  Converted by chemical/ physical means into useful products. Examples include coal, oil, natural gas, air, limestone, sand, metal ores, water WASTE PRODUCTS  No use or market for the product. Disposal can be a problem if they are toxic or produced in large amounts. 13

BY PRODUCTS  Not the main product, but do have a use either within the plant or commercially. E.g. sulfur dioxide from metal smelters 14

 Most occur in the earth’s crust as minerals  The most common occurrences are  K, Ca, Na, Mg as salts(Cl –, SO 4 2–, CO 3 2– )  Al, Fe, Sn as oxides  Zn, Ni, Pb, Cu as sulfides  Au, Ag, Pt as the uncombined metal 15

 When metals react they undergo oxidation (lose electrons) M  M x+ + xe  More easily a metal is oxidised, the less easily its ions are reduced to the metal  When determining the reactivity of a metal its reactions with water, acid and metal displacement reactions are considered 16

 Example: Reactions of Calcium  Water: Ca (s) +H 2 O (l)  Ca(OH) 2(s) + H 2(g)  Acid: Ca (s) + 2H + (aq)  Ca 2+ (aq) + H 2(g)  Displacement: Ca (s) + Zn 2+ (aq)  Ca 2+ (aq) + Zn (s) 17

 Ore deposit is a region in the earth’s crust where the concentration of a metallic mineral is at a level where the extraction of the metal is commercially viable 18

 Concentration of the mineral (removal of the gangue)  Conversion of the concentrate into a substance suitable for reduction. (Most common chemical process metal sulfide to metal oxide)  Reduction of the metal compound to metal via chemical means or electrolysis.  Refining the metal to remove trace impurities 19

 Zinc ore (zinc blende) is mined at Broken Hill (NSW) and Mt Isa (Qld). Contains approx 2-8% zinc  Crushed and ground into small particles at the mine ready for froth flotation 20

 Ore is added to tanks containing water, frothing agents and collector molecules (molecules with polar and non polar ends)  ZnS is attracted to the polar end of collector molecules and is carried to the surface of tanks on the froth when air is blown through the mixture. This is skimmed off.  Gangue remains on the bottom of the tank as a sludge 21

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 The zinc sulfide is roasted in air to form zinc oxide 2ZnS (s) + 3O 2(g)  2ZnO (s) + 2SO 2(g)  Sulfur dioxide is used to make sulfuric acid for next step (Contact process)  Oxide is leached with sulfuric acid ZnO (s) + H 2 SO 4(aq)  ZnSO 4(aq) + H 2 O (l) 23

 Zinc powder is added to displace less reactive metals (Ag +, Cd 2+, Cu 2+ ). These are collected and processed. Electrolysis of zinc sulfate  Anode (Lead or silver/lead) 2H 2 O (l)  O 2(g) + 4H + (aq) + 4e  Cathode (aluminium or zinc) Zn 2+ (aq) +2e  Zn (s) 24

 Overall 2Zn 2+ (aq) +2H 2 O (l)  2Zn (s) +O 2(g) + 4H + (aq)  The zinc produced is 99.95% pure and requires no further purification 25

 Metals more active than zinc can’t be produced by electrolysis of aqueous solutions.  If a solution of a more active metal is electrolysed then 2H 2 O (l) + 2e  H 2(g) + 2OH – (aq) occurs at the cathode in preference to the reduction of the metal.  A molten electrolyte is required with metals above zinc 26

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 Molten alumina Al 2 O 3 is mixed with cryolite Na 3 AlF 6, CaF 2 and AlF 3.  This mixture has a melting point of ~1000 o C compared to alumina which melts at 2030 o C  This means the electrolysis is carried out at a lower temperature saving money 28

Anode (Carbon)  2O 2– (l)  O 2(g) +4e  C (s) + O 2(g)  CO 2(g)  The anode is eaten away and requires regular replacement. Cathode (Carbon lined steel tank)  Al 3+ (l) + 3e  Al (l)  The aluminium forms below the molten electrolyte and can be tapped off. 29

Overall  4Al 3+ (l) +6O 2– (l) +3C (s)  4Al (l) + 3CO 2(g) 30

 Metals below aluminium can be produced by reduction with carbon  Iron: 3C (s) + Fe 2 O 3(s)  2Fe (s) + 3CO (g)  Zinc: C (s) + ZnO (s)  Zn (s) + CO (g)  These metal are more easily reduced than metals higher in the reactivity series 31

 The Reduction stage consumes most energy and so is the most costly stage of any metal production.  Electrolysis of a molten (non aqueous) electrolyte requires the more energy than other methods of reduction.  Consequently it is preferable (cost wise) if a metal can be either chemically reduced or produced by electrolysis of an aqueous solution. 32

 Chemical Reduction  Electrolysis of aqueous solution  Electrolysis of molten liquid 33 Most Energy required: Most expensive Least Energy required: Least expensive