Learn the assorted cut downing agents, apart from C, used in obtaining metals such as H, aluminum in alumino-thermite procedure, and electrolytic decrease in both aqueous and non-aqueous media.
Learn some methods of refinement of metals such as: Bessemerization Liquation, Cupellation, Hydrometallurgy, Vapour-phase refinement ( van Arkel-de Boes procedure, M and procedure ) , zone refinement and electrolytic refinement.
Grok the importance of thermodynamics in the metallurgical procedures particularly the decrease of oxides.
Understanding Ellingham diagrams with mention to oxide ores and their Iraqi National Congress to choose the appropriate reduction agent.
CROSS CURRICULAR LINKS
Biology – To analyze the importance of metals in prolonging life.
Physicss – To foreground the applications of Si and Ge in semiconducting material
devices after obtaining them in ultrapure province.
Geology – To cognize how metals occur in the Earth ‘s crust.
MIND – Map
Concentration of ores
Physical and Chemical Methods
Conversion of ore to oxide signifier
Decrease of ore to crude metal
Choice or cut downing agent. Carbon Aluminium Electric Current
Refining of Crude Metal
Liquation Cupellation Bessernerzation Hydrometollurgy
Vapour Phase refinement
( Van Arkel and Mind Process )
Zone refinement electrolytic refinement.
Thermodynamicss or metallurgical procedures
Gibbs Energy Ellingham diagrams
UNIT – Six
GENERAL PRINCIPLES AND
PROCESSES OF ISOLATION OF ELEMENTS
Introduction to Metallurgy
Our planet Earth is a huge beginning of elements which are distributed in its crust, H2O organic structures and atmosphere. Out of these elements about 80 per cent are metals which occur either in the combined province or in free province ( called motivation province ) . Metallic elements happening in free province are Cu, Ag, gold and Pt group metals. Not lone metals some non-metals besides occur in the free province, such as, C, sulfur, N, O and group 18 elements ( the baronial gases ) . Apart from metals and non-metals some elements occur as metalloids which show both the belongingss of metals and non-metals. Metalloid Si is the anchor of electronic industry and solar cells.
Distribution of elements in the above three classs in shown in the periodic Table ( Fig. 6.1, Ref www.wikipedia.org )
Some most abundant elements in the combined signifier as solutes are:
In Earth crust In sea H2O
O, Si, Al, Fe, Cl- , Na+ , SO42-
Ca, Na, K and Mg MG2+ , Ca2+ and K+
Some life back uping metals are Fe, Ca and Mg. Chlorophyll, a compound of Mg, is responsible for the photosynthesis procedure in let go ofing O.
General rules of metallurgy
For any application of a metal it has to be produced in a pure province. Here lies the importance or metallurgy. Metallurgy involves the initial purification and concentration of the ore and its subsequent decrease to metal.
Minerals and ores
Naturally happening beginnings of metals are called minerals which are by and large contaminated with drosss such as yearss and silicious affair.
A mineral which is rich in the metal compound and which can be used to pull out metal economically is termed as an ore. Therefore, all ores are minerals but all minerals are non ores. The drosss which are by and large present in ores are called gangue.
Following is the list of some of import ores of a few metals:
Iron ( Fe )
Photograph of metals
Aluminium ( Al )
Photograph of metals
Na3 Al F6
Copper ( Cu )
Photograph of metals
Malachite ( Green )
Cu Fe S2
CuCO3. Cu ( OH ) 2
Photograph of metals
Zinc ( Zn )
From the above list of ores and besides from literature ( www.wikipedia.org )
You will happen that metals by and large occur as:
Stairss in the extraction of metals
Concentration of ore
Decrease of ore
( Chemical decrease or electrochemical decrease )
Refining of metal
Concentration of ore
Ores are normally contaminated with sand and clay minerals called gangue. Therefore, the first measure to obtain the metal from the ore is to take every bit much gangue as possible. To make so the ore is crushed to ticket atoms and subjected to the undermentioned methods of concentration:
Froth floatation method
Hydraulic lavation is done with an upward flow of H2O. In this procedure lighter gangue atoms are washed off go forthing behind the desired heavy are atoms.
This method is based on the different magnetic behaviour of gangue atoms and the ore. The conclutration of ore is done by seting the dried crushed ore on a conveyer belt traveling around a powerful magnetic roller. In this manner the ore is separated from the gangue atoms. As an illustration, magnetic iron-ore is ferromagnetic and on ( Fe3O4 ) .
Passing over a magnetic roller it gets carried off and made free from non-magnetic gangue.
Fig. 6.2 Magnetic separation
This method is designed for the concentration of sulphide ores. The method is based on the comparative denseness of gangue atoms and ore atoms. Either of two can be made to drift on the aqueous surface with air bubbles and be collected. This is achieved by adding some chemical compounds in H2O. The agreement is shown is Fig. 6. Air is blown with force per unit area to make froth which engulphes either the gangue or ore atoms. Following compounds:
Frothers: Man-made detergents, pine, oil, eucalyptus oil or coal pitch.
Collectors: Ten anthates.
These impart H2O repellant belongingss to the surface of the ore atoms to be floated.
Froth Stabilizers: Cresols and aminobenzine.
Sedatives: Sodium nitrile.
The intent of a sedative is to do uneffective one constituent of the assorted ore. For illustration, from a mixture of ZnS ( zinc blende ) and PbS ( galena ) ZnS is NaCNwhile heavier PbS atoms float on the surface.
Leaching is extration of an active ingradient of the low class ore. This is done by fade outing the coveted constituent in a suited chemical solution. [
Leaching of low class carbonate and oxide ores of Cu by dilute sulfuric acid:
CuCO3 ( S ) + H2SO4 ( aq ) > CuSO4 ( aq ) + CO2 ( g ) + H2O ( cubic decimeter )
CuO ( S ) + H2SO4 ( aq ) > CuSO4 ( aq ) + H2O ( cubic decimeter )
Leaching of amphiprotic arebauxide ( Al2O3 ) with hot aqueous Na hydrated oxide when drosss such as Fe2O3 and silicates remain
Al2O3 ( S ) + 2NaOH ( aq ) + 3H2O ( cubic decimeter ) –
2Na [ Al ( OH ) 4 ] aq
Na [ Al ( OH ) 4 ] is converted to pure Al2O3 by go throughing CO2 gas and heating the merchandise 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 Ag with aqueous Na nitrile solution in the presence of air:
4 Au ( S ) + 8NaCN ( aq ) + O2 ( g ) + 2H2O ( cubic decimeter ) > 4Na [ Au ( CN ) 2 ] ( aq ) + 4NaOH ( aq )
Ag ( S ) + 8NaCH ( aq ) + O2 ( g ) + 2H2O ( cubic decimeter ) > 4Na [ AgKN ) 2 ] ( aq ) + 4NaOH ( aq )
The several metals can be obtained by adding Zn which is a more positively charged metal than either gold or Ag:
2Na [ Au ( CN ) 2 ] ( aq ) + Zn ( S ) > Na2 [ Zn ( CN ) 4 ] ( aq ) + 2 Au ( S )
Conversion of ore to oxide
Metallic elements used in immense sums by and large occur as sulfides, oxides or carbonates. For sulfide and carbonate ores it is necessary to change over them into oxide signifiers prior to their decrease to metals. This transition is necessary due to the undermentioned ground:
Handiness of a less dearly-won cut downing agent
The cut downing agent should non interact chemically with the metal produced.
Handiness of a suited furnace.
The production of metal should be cost effectual.
There is barely a reduction agent which meets all the above demands. Electropositive metals such as Mg, Ca and aluminum can be used for the chemical decrease of oxide ores. These metals can non be used for the big scale production of less positively charged metals because of their high cost. However, C as coke tantrums good as a reduction agent within the above listed parametric quantities. Its oxide, C monoxide is besides a really good reduction agent. The efficaciousness of C monoxide as a cut downing agent additions with the addition in temperature. One serious drawback of coke is that it reacts with many passage metals and some non-transition metals at higher temperatures to organize carbides. However, C as coke and C monoxide remain the two versatile cut downing agents for Fe ores.
For C to be used as a reduction agent the sulfide or carbonate ores have to be converted into their several oxide signifiers. Carbon does non cut down sulfide ores to give metals. To happen out the ground see the following two decrease reactions:
2MS ( S ) + C ( S ) 2M ( cubic decimeter or S ) + CS2 ( g ) ……… . ( I )
( sulphide signifier )
MO ( S ) + C ( S ) M ( cubic decimeter or S ) + CO ( g ) ……… ( two )
( Oxide signifier )
For these two decrease reactions by C the Gibb ‘s energy of the reaction should be negative. This can go on merely when a?†G for CS2 will be more negative than a?†G for MS ( first reaction ) ; and for the 2nd reaction a?†G for CO should be more negative than a?†G for MO. Thermodynamically the first reaction where CS2 is formed is non executable, but the record reaction is executable. It may be noted that CS2 is really much less stable than CO gas. Therefore, the sulfide ores are foremost converted into the oxide signifier before cut downing them with coke.
This is done by heating the sulfide ores in the presence of roasting the sulfide Oregons is that a byproduct sulfur dioxide ( SO2 ) is obtained which is used to fabricate sulfuric acid.
To acquire the ores into their several oxide signifiers following procedures are used:
Calcination is heating the ores in the absence of air. This method is used for the carbonate, hydrated oxide 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 by and large done is a reverberatory furnace ( Fig. 6. Ref www.wikipedia.org ) . This procedure makes the ore procedure and easy feasible.
Roasting is heating the ores in the presence of air. This is done chiefly for sulphide ores:
2 Fe S2 ( S ) + 5O2 ( g ) > 2FeO ( S ) + 2SO2 ( g )
( press fool’s gold )
2Cu2S ( S ) + 3O2 ( g ) > 2Cu2O ( S ) + 2SO2 ( g )
( Cu glimpse )
2ZuS ( S ) + 3O2 ( g ) > 2PbO ( S ) + 2SO2 ( g )
( Galena )
Roasting is done in reverberatory furnace ( Fig. 6.4 Fef. www.wikipedia.org )
Roasting besides removes volatile drosss like sulfur, arsenic and P 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
Metallic elements used in an ordinary fibril bulb
Pull the figure or an ordinary bulb
Label assorted metals used in it
Give ground as to why tungsten metal is used as the fibril
Student Worksheet – 1
Which metal is liquid at room temperature
Leaching is by and large used for the undermentioned ores of metals
In Aluminium-thermite procedure the reduction agent used is
Heating of ores in the absence of air is known as
Froth floatation procedure is used to concentrate the undermentioned ore
how do metals happen in nature by virtuousness of their responsiveness
giving chemical equations describe the procedure of calcinations and roasting, severally.
Why are sulphide ores roasted to their oxide signifiers before their decrease with coke?
Describe the rule of leaching with suited illustrations.
Describe the rule of froth floatation procedure. How is PbS ore concentration ewhen it is contaminated with ZnS?
A mineral with high concentration of metal compound which is used to pull out metal productively.
Happening of metals in nature
Undesired stuffs present in ore.
Procedure of isolation of metals from ores affecting the stairss:
Concentration of ore
Decrease of ore to metal
Purification of metal
Concentration of ore
Froth flotation ( for sulfide ores )
Extraction with a suited dissolver for low class ores.
Heating of ores ( carbonate or hydrated oxide ) in the absence of air.
Heating of ores ( sulphide ores ) in the presence of air.
Industrial decrease procedure to obtain metal from ore.
Reducing agents used in smelting
Carbon as coke
Aluminum ( In Alumino-thermite procedure
Refining of petroleum metal
Besemerization ( known as oxidative refinement )
Vapour stage ( van Arkel and de Boer, and Mond procedures ) .
Zone refinement ( for Si )
Curves of Gibb ‘s energy V temperature. Used to choose a suited reduction agent.
Categorization of ores on the footing of the metal compounds
Concentration of ores on the footing of their chemical nature
Decrease of ore to acquire the metal taking a suited reduction agent
Purification of petroleum metal based on the nature of drosss present
A mineral holding 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 byproduct during roasting. SO2 gas
Extraction of low class ores. Leach
Concentration of ore by turn outing air bubbles. FROTH FLOTATION
A furnace used for the smelting of Fe ore. BLAST FURNACE
Procedure of decrease of metal oxides by aluminum. ALUMINO-THERMITE Procedure
Procedure used to obtain really high pure Si. ZONE Refining
Carbon monoxide is used to sublimate Ni. MONDS PROCESS
Zirconium tetraiodide ( Zrl4 ) bluess are decomposed on het tungsten fibril. ARKEL-DE BOER PROCSS
Sodium is obtained by go throughing electric current in liquefied Na chloride. ELECTROLYTIC REDUCTION
ADDITIONAL RESOURCE LINKS
Decrease of ore to crude metal
By utilizing the procedure of decrease, roasted or calcined ores are converted to crude metal. Different cut downing agents are used depending upon the reaction between the metal oxide and the reduction agent.
Decrease with C: FeZO3, CuO, ZuO, SuO2, PbO etc.
Decrease with Aluminum: FeZO3, Cr2O3, Mn3O4, TiO2 etc.
Decrease with Magnesium: B2O3, TiCl4, etc
Decrease with H: WO3, MOO3, GeO2, CO3O4 etc
Decrease with CO: Fe2O4, FeZO3, PbO, CuO
Electrolytic decrease: Electrolyzing of oxides, hydrated oxides or
chlorides in amalgamate province.
Smelting: This is a procedure in which oxide of a metal is assorted with coke and a suited flux. The mixture is heated to a high temperature in a blast furnace. Iron, Copper, Zinc and Sn can be obtained by this procedure. Carbon is a good reduction agent below 983K where every bit above this temperature CO acts as cut downing agent.
ZnO ( S ) + C ( S ) Zn ( S ) + CO ( g )
+ 2C ( S ) Sn ( S ) + 2CO ( g )
Fe2 + 3C ( S ) 2Fe ( S ) + 3CO ( g )
CuO ( S ) + C ( S ) Cu ( S ) + CO ( g )
A flux is a substance which is added to roated or calcined ore during smelting to take the non-fusible drosss of metallic oxides, silicon oxide, and silicates etc. During smelting flux combines with the non-fusible dross to change over it into fusible stuff called scoria. The scoria being light float over the liquefied metal from where it is removed.
Flux is of two types:
Acidic flux – SiO2:
Basic flux – Lime rock ( CaCO3 ) and Magnetite ( MgCO3 )
SiO2 + MgCO3 MgSio3 +
SiO2 + CaCO3 CaSiO3 +
Hydrometallurgy: Copper, Silver and gold are extracted by this procedure. The procedure is based on the rule that more positively charged metal can displace less electro positive metal from its salt solution. The 1 is treated with such seagents that the metal forms a soluble compound. On adding more positively charged metal to the solution, the less positively charged metal nowadays in the solution is precipitated.
Example: Extraction of Copper: Malachite ore is roasted and oxide formed is dissolved in sulfuric acid. On adding bit Fe to the solution, Cu is precipitated.
Cu ( OH ) 2. CuC > 2CuO ( S ) + H2O ( P ) + C
CuO ( S ) + H2S > CuS +
CuS + Fe ( S ) > Cu ( S ) + FeS
Extraction of Ag: ore is dissolved in NaCN solution and air is blown followed by add-on of Zinc turnings. Silver is precipitated.
Ag2S + 4NaCN > 2Na [ Ag ( CN ) 2 ] + Na2S
2Na [ Ag ( CN ) 2 ] + Zn > Na2 [ Zn ( CN ) 4 ] + 2Ag
Acid flux – used to take basic drosss
Basic flux – used to take acidic drosss
Decrease with H: Some of he metal oxides ( largely passage metals ) can respond with C at high temperatures to give metal carbides which resist farther oxidization. Oxides of these metal, are better reduced by H 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 little graduated table as H is extremely explosive.
Aluminium decrease method: This method is besides called Alumino-thermite procedure. Some of the metal oxides can non be reduced by C as affinity of O for the metal is more than for C, besides, metal may organize carbide at high temperature. Such metallic oxides are reduced by utilizing aluminium pulverization. The reaction is initiated by the utilizing Ba per oxide and a little piece of Mg thread.
Cr2 + 2Al ( S ) 2Cr ( P ) + Al2
Fe2 + 2Al ( S ) 2Fe ( P ) + Al2
3Mn3 + 8Al ( s ) 9Mn ( P ) +4Al2
Function of BaO2 is to supply O to magnesium when batch of heat is volved which initiates the thermite procedure.
Sulphide ores of less electro positive metals such as Hg, Pb and Cu etc are heated in air to partly change over the ore into oxide which so reacts with the staying sulfide in absence of air to give the metal and SO2 gas.
2HgS ( S ) +3 2HgO + 2S
2HgO ( S ) +HgS ( S ) 3Hg + S
Chemical reaction on p-5
This procedure may besides be called ante decrease procedure.
2PbS + 3O2 2PbO + 2S
2Pbu + PbS 3Pb + S
2Cu2S + 3O2 2Cu20 + 2S
2Cu20 + Cu2S 6Cu + S
Decrease by Electrolysis: The oxides of extremely positively charged metals of group I, II and Al component of group etc can non temperatures and these can organize carbides. These metals are obtained by electrolysis of their oxides, hydrated oxides or chlorides in amalgamate province. To take down the merger temperatures or to increase the conduction or both a little sum of other salt is added. The metal is liberated at cathode.
Sodium metal is obtained by electrolysis of amalgamate mixture of Nacl and Cacl2 ( down ‘s procedure ) or by electrolysis of amalgamate Na hydrated oxide ( Costner ‘s procedure ) .
Nacl > Na+ + cl-
At anode cl- > Cl + e-
Cl + chlorine > degree Celsius
At Cathode Na+ + e- > Na ( cubic decimeter )
Aluminium metal is obtained by electrolysis of amalgamate mixture of aluminum oxide 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 ( cubic decimeter )
Anode gets cosseted by O liberated during electrolysis, which needs replacing from clip to clip.
Refining of metals: Metallic elements obtained by any of the decrease method except electrolytic decrease contains drosss. Refining of metals is procedure where by unsought drosss present in the metals are removed. Different polishing procedures may be applied depending upon the nature of the metal and nature of drosss.
Name of the Procedure
Metallic element to be refined
Low runing metals like Sn, Pb, Bi and Hq etc.
Silver incorporating lead.
( Impure silver incorporating lead is heated in bone-ash cup made of bone ash or cement and a blast of air is passed over the liquefied mass. The drosss are oxidized and removed with the blast of air )
Fe and Cu
Vapour stage refinement
There are two methods
Mond ‘s procedure
Impure Ni is heated with CO ( g ) at 323K when volatile Ni ( CO ) 4is formed. These bluess of Ni ( VO ) 4are passed into another chamber maintained at 306K when Ni ( CO ) 4decomposes to pure Ni which gets deposited on little 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, bring forthing volatile T1I4, , ZrI4or BI3. These bluess are passed over electrically heated fibril of Tungsten. The blues decompose, metal gets deposited over the fibril and I liberated is — — – .
Ti ( S ) + 2TiTi ( s ) + 2
Zr ( S ) + 2ZnZr ( s ) + 2
2B ( S ) + 32B> 2B ( s ) + 3
Highly pure Si or gernanium required for doing semi-conductors are refined by this method. The impure rod of Si or Ge is surrounded by a warming cir-l which can travel from one terminal to another. The warmer is allowed to travel in one peculiar way. As the warmer moves off, the metal capitalizes and drosss move along the way of the motion of the warmer. The procedure is repeated a figure of times when a little part of the rod gets purified. The terminal part of the rod holding high concentration of drosss can be cut and disconded.
Most of the metals like Cu, Ag, gold, aluminum, lead etc are refined by this procedure. The impure metal is made the anode and a thin sheet of pure metal is made a cathode. The electrolytic solution consists by and large of an aqueous solution of a salt incorporating some acid or a composite of the metal.
Purification of Copper
Anode – Impure Cu
Cathode – Thin sheets of pure Cu
Electrolyte – An aqueous solution of Cu sulfate incorporating some H2SO4.
Purification of Silver
Anode: Impure Ag
Cathode: Thin sheet of pure Ag
Electrolyte – An aqueous solution of ASNO3containing HNO3.
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 Sn metal
Electrolyte – An aqueous solution of SNSO4containing H2S1F6.
Thermodynamicss of Metallurgical procedure: The metals are extracted when their oxides are heated with C or other metal and by thermic decomposition. For any self-generated reaction, the Gibb ‘s anergy alteration a?†G must be negative at a peculiar temperature.
a?†G = a?†H – Ta?†S
a?†H is enthal by alteration during the reaction, T is the absolute temperature and alteration during the reaction, T is the absolute temperature and a?†S is the entropy alteration during the reaction. The reaction will processed merely when a?†G is negative. For reaction where a?†H is negative and a?†S is positive. The reaction returns even at low temperatures.
Theoretically, it is possible to break up all metal oxides if sufficiently high temperature is come-at-able but oxides of Ag, An and Hg are the lone oxides which can be decomposed at easy come-at-able temperatures. Hence these metals are obtained by thermic decomposition of their oxides.
The pick of cut downing agent to obtain the metal from its oxide depends upon the alteration in Gibb ‘s energy a?†G. The secret plan of Gibb ‘s energy alteration versus temperature is called.
Ellingham disgram: There diagrams can be drawn for different compounds such as oxides, sulfides, halides etc. utilizing these diagrams one can do a pick of cut downing agent and the corresponding temperature at which, the reaction becomes executable. a?†G for the reaction is -ve.
Some outstanding characteristics of Ellingham diagram are:
The incline for metal to metal oxide is upward as Gibbs energy alteration decreases with addition of temperature.
The all follow a consecutive line unless they melt or zap. When alteration in information is big, the incline of line besides alterations for illustration the Hg-HgO line alterations slope at 629K when quicksilver Scophthalmus rhombuss and likewise Mg-MgO alterations slope at 1393K.
When temperature is increased, the graph crossed the line a?†G=0 at a peculiar temperature. Below this temperature, a?†G being negative, oxide is stable where every bit above this temperature a?†G is positive and the oxide become unstable. Thus it should break up into metal and O.
In a figure of decrease procedures, one metal is used to cut down the oxide of the other metal. Any metal can cut down the oxide or the another metal which lie above it in Ellingham diagram.
Ellingham diagrams give an indicant whether the reaction is possible or non. These graphs do non foretell the dynamicss of the reaction. This is a major restriction of Ellingham diagrams.
Ellingham diagram of C: Carbon reacts with O to give two oxides
C ( S ) + O2 ( g ) > CO2 ( g )
2C ( S ) + O2 ( g ) > 2CO ( g )
Carbon monoxide can foster respond with O to give C dioxide.
2CO ( g ) + O2 ( g ) > 2CO2 ( g )
When C alterations to carbon dioxide, alteration in information ( a?†S ) is really little and a?†G barely shows alterations with increasing temperature. The graph of a?†G against T is about horizontal.
When C alterations to carbon monoxide, a?†S is positive and a?†G becomes more negative with increasing temperature. As a consequence, the line shows downward incline. The two lines for C to carbon-dioxide and C 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 sulfide: Some metals occur in nature as sulfides, such as ZnS, CuS and PbS. The reaction for the decrease of these sulfides with C is extremely
2MS ( S ) + C ( S ) > 2M ( S ) + CS2 ( g )
unfavorable energetically because of the instability of C disulphide. It being an endothermal reaction, sulphide ores are roasted to oxides and their reduced into metals.