1.

Thevalue ofDelta _fG^(@)for formationofCr_2O _ 3is-540kJ mol^(-1)andthat ofAl_2O _ 3is- 827 kJ mol ^( - 1).Is thereductionofCr_2O _ 3possiblewithaluminium ?

Answer»

Solution :Thetwoequationsare :
`( 4 )/(3)Al (s)+O _ 2(g) to(2)/(3)Al_ 2O _ 3 (s),Delta_fG_(Al, Al_2O_3) ^(@) =- 827 KJ mol^(- 1) "" `… (i)
` (4)/(3)Cr (s)+O _2(g) to(2)/(3)Cr_ 2O _ 3(s) ,Delta_ FG^(@)=- 540 kJmol^(-1) "" `...(ii)
SubtractingEq. (ii) fromEq.(i),we have,
` (4)/(3) Al(s) +(2)/(3)Cr _2O_ 3(s)to( 2) /(3) Al _2O_ 3(s)+(4)/(3) Cr(s) ,Delta_ rG^(@) =-287 kJmol^(- 1 ) `
SINCE`Delta _r G^(@) `ofthecombinedredoxreactionis`- ve`,THEREFORE, reductionof` Cr_ 2O_3`byAl ispossible.


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