Thursday, September 5, 2019

Is Othello a Victim or Villain?

Is Othello a Victim or Villain? This is a play about Othello, a Moorish general in the Venetian army. He is the ultimate villain in this play as opposed to Iago, the high ranking soldier. Most would agree as a matter of fact that Iago is undoubtedly the villain of this tragic story. In order to perceive this, a superficial assessment of the two main characters in the play; Othello and Iago, should be made. The art of analysis on its own rejects the simple easy explanations but rather deals in the complex and mystifying facts. Although Iago is the natural nuisance and thus the obvious bad guy, his destiny is to create the tragedy that this play later becomes. A lengthy consideration in addition to an open mind will show the truth of the matter. Othello is the actual villain. Even though he initially lacks any malicious thoughts and ideas, he eventually gets to become a murderer due to emotionally untrustworthy and jealousy. As you read the play it is not common to associate Othello with such descriptive words as conceited, though he is in every sense of the word. As the plot unfolds it is already clear that Othello is going to fall from grace in a huge way and his undoing will be his insatiable ego. He knows his abilities as a great warrior and his superb sword wielding abilities. His prowess on the battle field raised his ranks to the brim of the military defenses of Venice city. He gained his lofty status due to his expertise as a military officer and with that came his conceit. When Iago tells him of the threats from Brabantio, he says, Let him do his spite: My services which I have done the signiory shall out-tongue his complaints (1509). He walks with an air of over confidence depicting tones of arrogance in saying that no one has the authority to accuse is reputation. And to add on to that he shows his lofty opinion, as lofty as it can be, by saying, I fetch my life and being from men of royal siege (1509). His head is swelling with the status and importance given to him by the men of power in the city of Venice. He starts to think he is infallible, great and unfaultable, thus weakening him to the crucial insights of his enemies as to what they should do to discredit Othello from grace, the Moor already changes with my poison: dangerous conceits are in their natures poisons (1555). Whilst Iago reveals his detailed plot, we come to discover another vice possessed by Othello, he has a jealous mind. This comes as a result of insecurities of his colour, his education and his age. I am black and have not those soft parts of conversation that clamberers have, for I am declined into the vale of years (1553). Othellos jealousy is fed by the aforementioned insecurities. He says, As he (Cassio) shall smile, Othello shall go mad; and his unbookish jealousy must construe poor Cassios smiles, gestures, and light behavior quite in the wrong (1569). Iago therefore only has to create an opportunity for Othellos jealousy to initiate his downfall. Finally, we take note of his emotional dishonesty. As soon as Iago plants his thoughts, Othellos head and heart quickly fills up with contempt and bitterness. He openly confesses his love for Desdemona but he is easily convinced otherwise by Iago due to his dishonest nature meaning he was not being truthful about his love for Desdemona. He says, If she be false, O then Heavn mocks itself: Ill not believe it (1554), This makes him sound like a passionate man yet afterwards gets mad and discredits Emilia as a simple bawd. (1557) since she says the Desdemona is faithful to him. This illustrates his love being no more that a sad illusion, simply an obsession to say the least. His emotional untruthfulness is connected to all his other vices and feeds of them creating a dangerous monster out on a once adorable and admirable man. However as much as Othello is the villain of the story, at more than one instance he has appeared to look like the victim as well. He appears to be a victim of his society and seems as though Iago toys with his irritable nature at his pleasure. Othello seems to be very gullible and at times very distant from the truth. He is innocent to the working mayhems and mischievous plans Iago comes up with. Othello loses his tempers easily as a child does when frustrated and Iago knew how to play with his shaky ego that amounted due to the thought that his wife is heating on him. And of course that is blatant lie. All the grace and gentleness that was Desdemona was easily mistaken for flirtations to the unsuspecting Othello. His uncontrollable temper and the proof caused the untimely death of his ever faithful wife. His reaction was like that of a child whose favorite toy had been snatched away. His anger does not even give him the time to listen to her side of the story and refuses to listen to her pleas of innocence. Though he has an evil side to him, Othello had turned into an insane state of mind and one could actually state that he might not have realized what he was doing until it was a little bit too late. While Othello might have some virtuous attributes, there is no doubt that his emotional dishonesty, jealousy and conceit all sum up to make him the ultimate villain of this Shakespearian classic play. In the end it is the unwitting prophecy Iago makes that comes true, O, beware, my lord, of jealousy; It is the green-eyed monster which doth mock the meat it feeds on; that cuckold lives in bliss Who, certain of his fate, loves not his wronger; But, O, what damned minutes tells he oer Who dotes, yet doubts, suspects, yet strongly loves!(1550). Yes, Iago should be the villain, but we hugely expect this of him, and he therefore lives up to just what we would expect.. The true bad guy, who gives this play its twist is Othello the disingenuous, suspicious and the proud Moor of Venice. Isolation of Elements: General Principles and Processes Isolation of Elements: General Principles and Processes Introduction to Metallurgy Our planet earth is a vast source of elements which are distributed in its crust, water bodies and atmosphere. Out of these elements nearly 80 per cent are metals which occur either in the combined state or in free state (called motive state). Metals occurring in free state are copper, silver, gold and platinum group metals. Not only metals some non-metals also occur in the free state, such as, carbon, sulphur, nitrogen, oxygen and group 18 elements (the noble gases). Apart from metals and non-metals some elements occur as metalloids which show both the properties of metals and non-metals. Metalloid silicon is the backbone of electronic industry and solar cells. Distribution of elements in the above three categories in shown in the periodic Table (Fig. 6.1, Ref www.wikipedia.org) Fig. 6.1 Some most abundant elements in the combined form as solutes are: In earth crust In sea water O, Si, Al, Fe, Cl-, Na+, SO42- Ca, Na, K and Mg MG2+, Ca2+ and K+ Some life supporting metals are iron, calcium and magnesium. Chlorophyll, a compound of magnesium, is responsible for the photosynthesis process in releasing oxygen. General principles of metallurgy For any application of a metal it has to be produced in a pure state. Here lies the importance or metallurgy. Metallurgy involves the initial purification and concentration of the ore and its subsequent reduction to metal. Minerals and ores Naturally occurring sources of metals are called minerals which are generally contaminated with impurities such as days and siliceous matter. A mineral which is rich in the metal compound and which can be used to extract metal economically is termed as an ore. Thus, all ores are minerals but all minerals are not ores. The impurities which are generally present in ores are called gangue. Following is the list of some important ores of a few metals: Metal Ore Chemical composition Iron (Fe) Photograph of metals Iron pyrites Hematite Magnetite FeS2 Fe2O3 Fe3O4 Aluminium (Al) Photograph of metals Bauxite Cryolite Al2O3 . 2H2O Na3 Al F6 Copper (Cu) Photograph of metals Copper pyrites Cuprite Malachite (Green) Cu Fe S2 Cu2O CuCO3 . Cu(OH)2 Photograph of metals Zinc (Zn) Calamine Zinc blende Zincite ZnCO3 ZnS ZnO From the above list of ores and also from literature (www.wikipedia.org) You will find that metals generally occur as: Oxides Sulphides Carbonates Halides Silicates Steps in the extraction of metals Concentration of ore Reduction of ore (Chemical reduction or electrochemical reduction) Refining of metal Concentration of ore Ores are usually contaminated with sand and clay minerals called gangue. Therefore, the first step to obtain the metal from the ore is to remove as much gangue as possible. To do so the ore is crushed to fine particles and subjected to the following methods of concentration: Hydraulic washing Magnetic Separation Froth flotation method Hydraulic washing Hydraulic washing is done with an upward flow of water. In this process lighter gangue particles are washed away leaving behind the desired heavy are particles. Magnetic separation This method is based on the different magnetic behavior of gangue particles and the ore. The conclutration of ore is done by putting the dried crushed ore on a conveyor belt moving around a powerful magnetic roller. In this way the ore is separated from the gangue particles. As an example, magnetite is ferromagnetic and on (Fe3O4). Passing over a magnetic roller it gets carried away and made free from non-magnetic gangue. Froth Flotation This method is designed for the concentration of sulphide ores. The method is based on the relative density of gangue particles and ore particles. Either of two can be made to float on the aqueous surface with air bubbles and be collected. This is achieved by adding some chemical compounds in water. The arrangement is shown is Fig. 6. Air is blown with pressure to create froth which engulphes either the gangue or ore particles. Following compounds: Frothers: Synthetic detergents, pine, oil, eucalyptus oil or coal tar. Collectors: X anthates . These impart water repellent properties to the surface of the ore particles to be floated. Froth Stabilisers: Cresols and aniline. Depressants: Sodium cyanide. The purpose of a depressant is to make ineffective one component of the mixed ore. For example, from a mixture of ZnS (sphalerite) and PbS (galena) ZnS is NaCNwhile heavier PbS particles float on the surface. Leaching Leaching is extration of an active ingradient of the low grade ore. This is done by dissolving the desired component in a suitable chemical solution.[ Example Are: Leaching of low grade carbonate and oxide ores of copper by dilute sulphuric acid: CuCO3(S) + H2SO4(aq) → CuSO4(aq) + CO2(g) + H2O(l) CuO(S) + H2SO4(aq) → CuSO4(aq) + H2O(l) Leaching of amphoteric arebauxide (Al2O3) with hot aqueous sodium hydroxide when impurities such as Fe2O3 and silicates remain Al2O3(S) + 2NaOH(aq) + 3H2O(l) 2Na[Al(OH)4] aq Na [Al (OH)4] is converted to pure Al2O3 by passing CO2 gas and heating the product Al(OH)3: Na[Al(OH)4](aq)+CO2(g) → Al(OH)3(S) + NaHCO3(aq) Al(OH)3(S) Al2O3(S) + 3H2O(g) Leaching of gold and silver with aqueous sodium cyanide solution in the presence of air: 4 Au(S) + 8NaCN(aq) + O2(g) + 2H2O(l) → 4Na[Au(CN)2](aq) + 4NaOH(aq) Ag(S) + 8NaCH(aq) + O2(g) + 2H2O(l) → 4Na[AgKN)2](aq) + 4NaOH(aq) The respective metals can be obtained by adding zinc which is a more electropositive metal than either gold or silver: 2Na [Au(CN)2](aq) + Zn(S) → Na2 [Zn(CN)4](aq) + 2 Au (S) Conversion of ore to oxide Metals used in huge amounts generally occur as sulphides, oxides or carbonates. For sulphide and carbonate ores it is necessary to convert them into oxide forms prior to their reduction to metals. This conversion is necessary due to the following reason: Availability of a less costly reducing agent The reducing agent should not interact chemically with the metal produced. Availability of a suitable furnace. The production of metal should be cost effective. Fewer impurities There is hardly a reducing agent which meets all the above requirements. Electropositive metals such as magnesium, calcium and aluminium can be used for the chemical reduction of oxide ores. These metals can not be used for the large scale production of less electropositive metals because of their high cost. However, carbon as coke fits well as a reducing agent within the above listed parameters. Its oxide, carbon monoxide is also a very good reducing agent. The efficacy of carbon monoxide as a reducing agent increases with the increase in temperature. One serious drawback of coke is that it reacts with many transition metals and some non-transition metals at higher temperatures to form carbides. However, carbon as coke and carbon monoxide remain the two versatile reducing agents for iron ores. For carbon to be used as a reducing agent the sulphide or carbonate ores have to be converted into their respective oxide forms. Carbon does not reduce sulphide ores to give metals. To find out the reason consider the following two reduction reactions: 2MS (S) + C(S) 2M (l or S) + CS2(g) †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦.(i) (sulphide form) MO (S) + C (S) M (l or S) + CO (g) †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ (ii) (Oxide form) For these two reduction reactions by carbon the Gibbs energy of the reaction should be negative. This can happen only when à ¢Ã‹â€ Ã¢â‚¬  G for CS2 will be more negative than à ¢Ã‹â€ Ã¢â‚¬  G for MS (first reaction); and for the second reaction à ¢Ã‹â€ Ã¢â‚¬  G for CO should be more negative than à ¢Ã‹â€ Ã¢â‚¬  G for MO. Thermodynamically the first reaction where CS2 is formed is not feasible, but the record reaction is feasible. It may be noted that CS2 is very much less stable than CO gas. Therefore, the sulphide ores are first converted into the oxide form before reducing them with coke. This is done by heating the sulphide ores in the presence of roasting the sulphide ors is that a by-product sulphur dioxide (SO2) is obtained which is used to manufacture sulphuric acid. To get the ores into their respective oxide forms following processes are used: Calcination Calcination is heating the ores in the absence of air. This method is used for the carbonate, hydroxide and hydrated ores CaCO3(S) CaO(S) + CO2(g) (calcite) MgCO3. CaCO3(S) MgO(S) + CaO(S) + 2CO2(g) (Dolomite) CuCO3. Cu(OH)2(S) 2CuO(S) + CO2(g) + H2O(g) (Malachite) Calcination is generally done is a reverberatory furnace (Fig. 6. Ref www.wikipedia.org). This process makes the ore process and easily workable. Roasting Roasting is heating the ores in the presence of air. This is done mainly for sulphide ores: 2 Fe S2 (S) + 5O2(g) → 2FeO(S) + 2SO2(g) (iron pyrite) 2Cu2S(S) + 3O2(g) → 2Cu2O(S) + 2SO2(g) (copper glance) 2ZuS(S) + 3O2(g) → 2PbO(S) + 2SO2(g) (Galena) Roasting is done in reverberatory furnace (Fig. 6.4 Fef. www.wikipedia.org) Roasting also removes volatile impurities like sulphur, arsenic and phosphorus as their volatile oxides: S(S) + O2 (g) → SO2(g) 4AS(S) + 3O2(g) → 2AS2O3(g) P4(S) + 5O2(g) → P4O10(g) Student Activity 1 Metals used in an ordinary filament bulb Draw the figure or an ordinary bulb Label various metals used in it Give reason as to why tungsten metal is used as the filament Student Worksheets Student Worksheet 1 Which metal is liquid at room temperature Aluminium Lead Mercury Zinc Leaching is generally used for the following ores of metals Lead Copper Iron Aluminium In Aluminium-thermite process the reducing agent used is Carbon Hydrogen Aluminium Sodium Heating of ores in the absence of air is known as Roasting Calcination Leaching Bensemerization Froth flotation process is used to concentrate the following ore Halide Silicates Sulphide carbonate how do metals occur in nature by virtue of their reactivity giving chemical equations describe the process of calcinations and roasting, respectively. Why are sulphide ores roasted to their oxide forms before their reduction with coke? Describe the principle of leaching with suitable examples. Describe the principle of froth flotation process. How is PbS ore concentration ewhen it is contaminated with ZnS? SUMMARY S. No. Description Ore A mineral with high concentration of metal compound which is used to extract metal profitably. Occurrence of metals in nature Oxides Sulphides Carbonates Silicates Gangue Undesired materials present in ore. Metallurgy Process of isolation of metals from ores involving the steps: Concentration of ore Reduction of ore to metal Purification of metal Concentration of ore Magnetic Froth floatation (for sulphide ores) Leaching Leaching Extraction with a suitable solvent for low grade ores. Calcinations Heating of ores (carbonate or hydroxide) in the absence of air. Roasting Heating of ores (sulphide ores) in the presence of air. Smelting Industrial reduction process to obtain metal from ore. Reducing agents used in smelting Hydrogen Carbon as coke Aluminium (In Alumino-thermite process Air Electrolytic Refining of crude metal Liquation Cupellation Besemerization (known as oxidative refining) Vapour phase (van Arkel and de Boer, and Mond processes). Zone refining (for silicon) Hydrometallurgy Electrolytic Ellingham diagrams Curves of Gibbs energy vs temperature. Used to select a suitable reducing agent. LOW CHART 1. 2. Classification of ores on the basis of the metal compounds Concentration of ores on the basis of their chemical nature 3. 4. Reduction of ore to get the metal choosing a suitable reducing agent Purification of crude metal based on the nature of impurities present Crossword A mineral having high concentration of a metal compound. ORE Heating or ore in the absence of air. CALCINATIONS Heating of ore in the presence of air. ROASTING Valuable by-product during roasting. SO2 gas Extraction of low grade ores. LEACHING Concentration of ore by proving air bubbles. FROTH FLOTATION A furnace used for the smelting of iron ore. BLAST FURNACE Process of reduction of metal oxides by aluminium. ALUMINO-THERMITE PROCESS Process used to obtain very high pure silicon. ZONE REFINING Carbon monoxide is used to purify nickel. MONDS PROCESS Zirconium tetraiodide (Zrl4) vapours are decomposed on heated tungsten filament. ARKEL-DE BOER PROCSS Sodium is obtained by passing electric current in molten sodium chloride. ELECTROLYTIC REDUCTION ADDITIONAL RESOURCE LINKS www.wikipedia.org Reduction of ore to crude metal By using the process of reduction, roasted or calcined ores are converted to crude metal. Different reducing agents are used depending upon the reaction between the metal oxide and the reducing agent. Reduction with carbon : FeZO3, CuO, ZuO, SuO2, PbO etc. Reduction with Aluminium : FeZO3, Cr2O3, Mn3O4, TiO2 etc. Reduction with Magnesium : B2O3, TiCl4, etc Reduction with hydrogen : WO3, MOO3, GeO2, CO3O4 etc Reduction with CO : Fe2O4, FeZO3, PbO, CuO Electrolytic reduction : Electrolyzing of oxides, hydroxides or chlorides in fused state. Smelting : This is a process in which oxide of a metal is mixed with coke and a suitable flux. The mixture is heated to a high temperature in a blast furnace. Iron, Copper, Zinc and tin can be obtained by this process. Carbon is a good reducing agent below 983K where as above this temperature CO acts as reducing agent. ZnO(S) + C(S) Zn(S) + CO(g) Zincite + 2C(S) Sn(S) + 2CO(g) Cassitesite Pondered anthracite Fe2 + 3C(S) 2Fe(S) + 3CO(g) Haemetite CuO(S) + C(S) Cu(S) + CO(g) A flux is a substance which is added to roated or calcined ore during smelting to remove the non-fusible impurities of metallic oxides, silica, and silicates etc. During smelting flux combines with the non-fusible impurity to convert it into fusible material called slag. The slag being light float over the molten metal from where it is removed. Flux is of two types: Acidic flux SiO2 : Basic flux Lime stone (CaCO3) and Magnetite (MgCO3) SiO2 + MgCO3 MgSio3 + SiO2 + CaCO3 CaSiO3 + Hydrometallurgy : Copper, Silver and gold are extracted by this process. The process is based on the principle that more electropositive metal can displace less electro positive metal from its salt solution. The one is treated with such seagents that the metal forms a soluble compound. On adding more electropositive metal to the solution, the less electropositive metal present in the solution is precipitated. Example: Extraction of Copper : Malachite ore is roasted and oxide formed is dissolved in sulphuric acid. On adding scrap iron to the solution, copper is precipitated. Cu(OH)2 . CuC → 2CuO(S) + H2O(P) + C CuO(S) + H2S → CuS + CuS + Fe(S) → Cu(S) + FeS Extraction of silver : ore is dissolved in NaCN solution and air is blown followed by addition of Zinc turnings. Silver is precipitated. Ag2S + 4NaCN → 2Na[Ag(CN)2] + Na2S 2Na [Ag(CN)2] + Zn → Na2 [Zn(CN)4] + 2Ag Solution Acid flux used to remove basic impurities Basic flux used to remove acidic impurities Reduction with hydrogen :Some of he metal oxides (mostly transition metals) can react with carbon at high temperatures to give metal carbides which resist further oxidation. Oxides of these metal, are better reduced by hydrogen gas. i.e. WO3 + 3H2 W + 3H2O(g) MOO3 + 3H2 Mo + 3H2O(g) GeO2 + 2H2 Ge + 2H2O(g) CO3O4 + 4H2 3Co + 2H2O(g) Using H2(G), metals are obtained in small scale as hydrogen is highly explosive. Aluminium reduction method: This method is also called Alumino-thermite process. Some of the metal oxides cannot be reduced by carbon as affinity of oxygen for the metal is more than for carbon, also, metal may form carbide at high temperature. Such metallic oxides are reduced by using aluminium powder. The reaction is initiated by the using barium per oxide and a small piece of Mg ribbon. Fig. Cr2 + 2Al(S) 2Cr(P) + Al2 Fe2 + 2Al(S) 2Fe(P) + Al2 3Mn3 + 8Al(s) 9Mn(P) +4Al2 Function of BaO2 is to provide oxygen to magnesium when lot of heat is volved which initiates the thermite process. Air reduction : Sulphide ores of less electro positive metals such as Hg, Pb and Cu etc are heated in air to partially convert the ore into oxide which then reacts with the remaining sulphide in absence of air to give the metal and SO2 gas. 2HgS(S) +3 2HgO + 2S 2HgO(S) +HgS(S) 3Hg + S Reaction on p-5 This process may also be called ante reduction process. 2PbS + 3O2 2PbO + 2S 2Pbu + PbS 3Pb + S 2Cu2S + 3O2 2Cu20 + 2S 2Cu20 + Cu2S 6Cu + S Reduction by Electrolysis : The oxides of highly electropositive metals of group I, II and Al element of group etc cannot temperatures and these can form carbides. These metals are obtained by electrolysis of their oxides, hydroxides or chlorides in fused state. To lower the fusion temperatures or to increase the conductivity or both a small amount of other salt is added. The metal is liberated at cathode. Sodium metal is obtained by electrolysis of fused mixture of Nacl and Cacl2 (downs process) or by electrolysis of fused sodium hydroxide (Costners process). Nacl → Na+ + cl- Fused At anode cl- → Cl + e- Cl + cl → c At Cathode Na+ + e- → Na(l) Aluminium metal is obtained by electrolysis of fused mixture of alumina and Gyolite (Na3[Al F6]) Na3 Al → 3Na F(P) + Al Al →Al3+ + 3F- At anode F- → F + e- F+F → F2(a) 2A+ 6 → 4Al + 3O2(g) At cathode Al3+ + 3e- → A(l) Anode gets cosseted by oxygen liberated during electrolysis, which needs replacement from time to time. Refining of metals: Metals obtained by any of the reduction method except electrolytic reduction contains impurities. Refining of metals is process where by undesired impurities present in the metals are removed. Different refining processes may be applied depending upon the nature of the metal and nature of impurities. Name of the Process Metal to be refined Liquation Low melting metals like Sn, Pb, Bi and Hq etc. Cupellation Silver containing lead. (Impure silver containing lead is heated in cupel made of bone ash or cement and a blast of air is passed over the molten mass. The impurities are oxidized and removed with the blast of air) Bessemerisation Fe and Cu Vapour phase refining There are two methods Monds process Impure Ni is heated with CO(g)at 323K when volatile Ni (CO)4is formed. These vapours of Ni(VO)4are passed into another chamber maintained at 306K when Ni (CO)4decomposes to pure Ni which gets deposited on small Ni balls kept in the chamber and carbon-monoxide gas is rejected. Ni(S)+4CO(g)Ni(CO)4Ni(S)+ 4CO(g) Van Arkel Process Ti, Zr, Hf, V, Th, B are refined by this method. Impure metal is heated with I2, producing volatile T1I4,, ZrI4or BI3. These vapours are passed over electrically heated filament of Tungsten. The vapours decompose, metal gets deposited over the filament and iodine liberated is . Ti(S)+ 2TiTi(s) + 2 Zr(S)+ 2ZnZr(s) + 2 2B(S)+ 32B→ 2B(s) + 3 Zone refining Highly pure silicon or gernanium required for making semi-conductors are refined by this method. The impure rod of silicon or germanium is surrounded by a heating cir-l which can move from one end to another. The heater is allowed to move in one particular direction. As the heater moves away, the metal capitalizes and impurities move along the direction of the movement of the heater. The process is repeated a number of times when a small portion of the rod gets purified. The end portion of the rod having high concentration of impurities can be cut and disconded. Electrolytic refining Most of the metals like copper, silver, gold, aluminium, lead etc are refined by this process. The impure metal is made the anode and a thin sheet of pure metal is made a cathode. The electrolytic solution consists generally of an aqueous solution of a salt containing some acid or a complex of the metal. Purification of Copper Anode Impure copper Cathode Thin sheets of pure copper Electrolyte An aqueous solution of copper sulphate containing some H2SO4. Purification of Silver Anode: Impure silver Cathode: Thin sheet of pure Ag Electrolyte An aqueous solution of ASNO3containing HNO3. Pb Anode: Impure metal Cathode: Sheet of pure lead Electrolyte A solution of PbS1F6containing 8-10 of H2S1F6. Purification of Sn Anode: Impure Tin Cathode: A sheet of pure tin metal Electrolyte An aqueous solution of SNSO4containing H2S1F6. Thermodynamics of Metallurgical process: The metals are extracted when their oxides are heated with carbon or other metal and by thermal decomposition. For any spontaneous reaction, the Gibbs anergy change à ¢Ã‹â€ Ã¢â‚¬  G must be negative at a particular temperature. à ¢Ã‹â€ Ã¢â‚¬  G = à ¢Ã‹â€ Ã¢â‚¬  H Tà ¢Ã‹â€ Ã¢â‚¬  S à ¢Ã‹â€ Ã¢â‚¬  H is enthal by change during the reaction, T is the absolute temperature and change during the reaction, T is the absolute temperature and à ¢Ã‹â€ Ã¢â‚¬  S is the entropy change during the reaction. The reaction will processed only when à ¢Ã‹â€ Ã¢â‚¬  G is negative. For reaction where à ¢Ã‹â€ Ã¢â‚¬  H is negative and à ¢Ã‹â€ Ã¢â‚¬  S is positive. The reaction proceeds even at low temperatures. Theoretically, it is possible to decompose all metal oxides if sufficiently high temperature is attainable but oxides of Ag, An and Hg are the only oxides which can be decomposed at easily attainable temperatures. Hence these metals are obtained by thermal decomposition of their oxides. The choice of reducing agent to obtain the metal from its oxide depends upon the change in Gibbs energy à ¢Ã‹â€ Ã¢â‚¬  G. The plot of Gibbs energy change versus temperature is called. Ellingham disgram: There diagrams can be drawn for different compounds such as oxides, sulphides, halides etc. using these diagrams one can make a choice of reducing agent and the corresponding temperature at which, the reaction becomes feasible. à ¢Ã‹â€ Ã¢â‚¬  G for the reaction is -ve. Some salient features of Ellingham diagram are: The slope for metal to metal oxide is upward as Gibbs energy change decreases with increase of temperature. The all follow a straight line unless they melt or vaporize. When change in entropy is large, the slope of line also changes for example the Hg-HgO line changes slope at 629K when mercury brills and similarly Mg-MgO changes slope at 1393K. When temperature is increased, the graph crossed the line à ¢Ã‹â€ Ã¢â‚¬  G=0 at a particular temperature. Below this temperature, à ¢Ã‹â€ Ã¢â‚¬  G being negative, oxide is stable where as above this temperature à ¢Ã‹â€ Ã¢â‚¬  G is positive and the oxide become unstable. Thus it should decompose into metal and oxygen. In a number of reduction processes, one metal is used to reduce the oxide of the other metal. Any metal can reduce the oxide or the another metal which lie above it in Ellingham diagram. Ellingham diagrams give an indication whether the reaction is possible or not. These graphs do not predict the kinetics of the reaction. This is a major limitation of Ellingham diagrams. Ellingham diagram of carbon: Carbon reacts with oxygen to give two oxides C(S) + O2(g) → CO2(g) 2C(S) + O2(g) → 2CO(g) Carbon monoxide can further react with oxygen to give carbon dioxide. 2CO(g) + O2(g) → 2CO2(g) When carbon changes to carbon dioxide, change in entropy (à ¢Ã‹â€ Ã¢â‚¬  S) is very small and à ¢Ã‹â€ Ã¢â‚¬  G hardly shows changes with increasing temperature. The graph of à ¢Ã‹â€ Ã¢â‚¬  G against T is almost horizontal. When carbon changes to carbon monoxide, à ¢Ã‹â€ Ã¢â‚¬  S is positive and à ¢Ã‹â€ Ã¢â‚¬  G becomes more negative with increasing temperature. As a result, the line shows downward slope. The two lines for carbon to carbon-dioxide and carbon to carbon monoxide cross at 983K. below this temperature formation of CO2 is favoured whereas above this temperatures formation of CO is preferred. Ellingham diagram of metal sulphide : Some metals occur in nature as sulphides, such as ZnS, CuS and PbS. The reaction for the reduction of these sulphides with carbon is highly 2MS(S) + C(S) → 2M(S) + CS2(g) unfavourable energetically because of the instability of carbon disulphide. It being an endothermic reaction, sulphide ores are roasted to oxides and their reduced into metals.

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