On the basis of standard electrode potential values, suggest which of the following reactions would take place? (Consult the book for `E^(ϴ)` value)
(a) `Cu+Zn^(2+)toCu^(2+)+Zn`
(b) `Mg+Fe^(2+)toMg^(2+)+Fe`
(c ) `Br_(2)+2Cl^(-)toCl_(2)+2Br^(-)`
(d) `Fe+Cd^(2)toCd+Fe^(2+)`

Explanation

(i) from the table
`E_(Cu^(2+)//Cu)=+0.34 V "and" E_(Zn^(2+)//Zn))^(@)=-0.76V` The reaction `Cu+Zn^(2+) rarr Cu^(2+)+Zn` is feasible if `E_("cell")^(@)` is +v in this cell buy gets oxidised to `Cu^(2+)` therefore `Cu^(2+)//Cu` redox couple acts as the anode further since `Zn^(2+)` gets reduced to Zn therefore `Zn^(2+)//Zn` acts as the cathode
`therefore E_(cell)^(@)=E_("anode")^(@)=E_(Cu(Zn^(2+)//Zn)^(@)=-0.76-0.34=-1.10 v`
since `E_("cell")^(@)` of the reaction `Cu+zn^(2+)rarrCu^(2+)rarrCu^(2+)Zn` is -ve therefore this reaction does not occur
(ii) from `E_(Mg^(2+)//Mg)^(@)=-2.37 v` and `E_(Fe^(2+)//Fe)^(@)=-0.74 V`
The reactoin `Mg+Fe^(2+)rarrMg^(2+)+Fe` is possible if `E_(cell)^(@)` is +ve here `Mg^(2+)//Mg` redox couple acts as the anode while `Fe^(2+)//Fe` acts the cathode
(iii) From `E_(Br^(-)//Br_(2))^(@)=+1.08 V` and `E_(CI^(-)//CI_(2))^(@)=+1.36 v`
The reaction `Br_(2)+21CI^(-)rarrCI_(2)+2Br^(-)` will occur if `E_(cell)^(@)`is +ve in this cel `Br_(2)//Br^(-)` redox couple wil acts as the cahode and `CI_(2)//CI^(-)` will act as the anode
`E_(cell)^(@)=E_("cathode")^(@)-E_("anode")^(@)=E^(2)_(Br^(2+)//Fe)=-0.74 V and E_(Cd^(2+)//Cd)^(@)=-0.44V`
The reaction `Fe+Cd^(2+)rarrCd+Fe^(2+)` wil occur if `E_(cell)^(@)` is +ve here in his reaction `Fe^(2+)//Fe` electrode will act as the anode while `Cd^(2+)//Cd` electrode will act as the cathode
`E_(cell)^(@)=E_(cathode)^(@)-E_(anode)^(@)=E_(Cd^(2+)//Cd)^(@)-e_(Fe^(2+)//Fe)^(@)rarrCd+Fe^(2+)` will occur