Important Electrochemistry Formulas for JEE and NEET

 Page 1


  
  
     
 
      
   
     
              
       
  
   
 
 
   
         
            
ELECTROCHEMISTRY
ELECTRODE POTENTIAL
For any electrode ? oxidiation potential = ? Reduction potential
E
cell
 = R.P of cathode ? R.P of anode
E
cell
 = R.P. of cathode + O.P of anode
E
cell
 is always a +ve quantity & Anode will be electrode of low R.P
Eº
Cell
 = SRP of cathode ? SRP of anode.
? Greater the SRP value greater will be oxidising power.
GIBBS FREE ENERGY CHANGE :
?G = ? nFE
cell
?Gº = ? nFEº
cell
NERNST EQUATION : (Effect of concentration and temp on emf of cell)
?G = ?Gº + RT ?nQ (where Q is raection quotient)
?Gº = ? RT ?n K
eq
E
cell
 = Eº
cell
 ? 
nF
RT
 ?n Q
E
cell
 = Eº
cell
 ? Q log
nF
RT 303 . 2
Page 2


  
  
     
 
      
   
     
              
       
  
   
 
 
   
         
            
ELECTROCHEMISTRY
ELECTRODE POTENTIAL
For any electrode ? oxidiation potential = ? Reduction potential
E
cell
 = R.P of cathode ? R.P of anode
E
cell
 = R.P. of cathode + O.P of anode
E
cell
 is always a +ve quantity & Anode will be electrode of low R.P
Eº
Cell
 = SRP of cathode ? SRP of anode.
? Greater the SRP value greater will be oxidising power.
GIBBS FREE ENERGY CHANGE :
?G = ? nFE
cell
?Gº = ? nFEº
cell
NERNST EQUATION : (Effect of concentration and temp on emf of cell)
?G = ?Gº + RT ?nQ (where Q is raection quotient)
?Gº = ? RT ?n K
eq
E
cell
 = Eº
cell
 ? 
nF
RT
 ?n Q
E
cell
 = Eº
cell
 ? Q log
nF
RT 303 . 2
  
E
cell
 = Eº
cell
 ? 
n
0591 . 0
 log Q [At 298 K]
At chemical equilibrium
?G = 0 ; E
cell
 = 0.
? log K
eq
 = 
0591 . 0
E n
o
cell
.
Eº
cell
 =
n
0591 . 0
 log K
eq
For an electrode M(s)/M
n+
.
nF
RT 303 . 2
º E E
M / M M / M
n n ? ? ? ? log 
] M [
1
n?
.
CONCENTRATION CELL :
A cell in which both the electrods are made up of same material.
For all concentration cell Eº
cell
 = 0.
(a) Electrolyte Concentration Cell :
eg. Zn(s) / Zn
2+
 (c
1
) || Zn
2+
(c
2
) / Zn(s)
E = 
2
0591 . 0
 log 
1
2
C
C
(b) Electrode Concentration Cell :
eg. Pt, H
2
(P
1
 atm) / H
+
 (1M) / H
2
 (P
2
 atm) / Pt
E = 
2
0591 . 0
 log ?
?
?
?
?
?
?
?
2
1
P
P
DIFFERENT TYPES OF ELECTRODES :
1. Metal-Metal ion Electrode M(s)/M
n+
 . M
n+
 + ne
?
 ?? ? M(s)
E = Eº + 
n
0591 . 0
 log[M
n+
]
2. Gas-ion Electrode Pt /H
2
(Patm) /H
+
 (XM)
as a reduction electrode
H
+
(aq) + e
?
 ?? ?
2
1
H
2
 (Patm)
E = Eº ? 0.0591 log 
] H [
P 2
1
H
2
?
Page 3


  
  
     
 
      
   
     
              
       
  
   
 
 
   
         
            
ELECTROCHEMISTRY
ELECTRODE POTENTIAL
For any electrode ? oxidiation potential = ? Reduction potential
E
cell
 = R.P of cathode ? R.P of anode
E
cell
 = R.P. of cathode + O.P of anode
E
cell
 is always a +ve quantity & Anode will be electrode of low R.P
Eº
Cell
 = SRP of cathode ? SRP of anode.
? Greater the SRP value greater will be oxidising power.
GIBBS FREE ENERGY CHANGE :
?G = ? nFE
cell
?Gº = ? nFEº
cell
NERNST EQUATION : (Effect of concentration and temp on emf of cell)
?G = ?Gº + RT ?nQ (where Q is raection quotient)
?Gº = ? RT ?n K
eq
E
cell
 = Eº
cell
 ? 
nF
RT
 ?n Q
E
cell
 = Eº
cell
 ? Q log
nF
RT 303 . 2
  
E
cell
 = Eº
cell
 ? 
n
0591 . 0
 log Q [At 298 K]
At chemical equilibrium
?G = 0 ; E
cell
 = 0.
? log K
eq
 = 
0591 . 0
E n
o
cell
.
Eº
cell
 =
n
0591 . 0
 log K
eq
For an electrode M(s)/M
n+
.
nF
RT 303 . 2
º E E
M / M M / M
n n ? ? ? ? log 
] M [
1
n?
.
CONCENTRATION CELL :
A cell in which both the electrods are made up of same material.
For all concentration cell Eº
cell
 = 0.
(a) Electrolyte Concentration Cell :
eg. Zn(s) / Zn
2+
 (c
1
) || Zn
2+
(c
2
) / Zn(s)
E = 
2
0591 . 0
 log 
1
2
C
C
(b) Electrode Concentration Cell :
eg. Pt, H
2
(P
1
 atm) / H
+
 (1M) / H
2
 (P
2
 atm) / Pt
E = 
2
0591 . 0
 log ?
?
?
?
?
?
?
?
2
1
P
P
DIFFERENT TYPES OF ELECTRODES :
1. Metal-Metal ion Electrode M(s)/M
n+
 . M
n+
 + ne
?
 ?? ? M(s)
E = Eº + 
n
0591 . 0
 log[M
n+
]
2. Gas-ion Electrode Pt /H
2
(Patm) /H
+
 (XM)
as a reduction electrode
H
+
(aq) + e
?
 ?? ?
2
1
H
2
 (Patm)
E = Eº ? 0.0591 log 
] H [
P 2
1
H
2
?
  
3. Oxidation-reduction Electrode Pt / Fe
2+
, Fe
3+
as a reduction electrode Fe
3+
 + e
?
 ?? ? Fe
2+
E = Eº ? 0.0591 log 
] Fe [
] Fe [
3
2
?
?
4. Metal-Metal insoluble salt Electrode eg. Ag/AgCl, Cl
?
as a reduction electrode  AgCl(s) + e
?
 ?? ? Ag(s) + Cl
?
Ag / AgCl / Cl
E ?
 = 
Ag / AgCl
0
/ Cl
E ?
 ? 0.0591 log [Cl
?
].
ELECTROLYSIS :
(a) K
+
, Ca
+2
, Na
+
, Mg
+2
, Al
+3
, Zn
+2
, Fe
+2
, H
+
, Cu
+2
, Ag
+
, Au
+3
.
 Increasing order of deposition.
(b) Similarly the anion which is strogner reducing agent(low value of SRP)
is liberated first at the anode.
diposition of order g sin Increa
, Br , Cl , OH , NO , SO
? ? ? ?
3
? 2
4
? ? ? ? ? ? ? ? ? ? ? ?
?
I
FARADAY?S LAW OF ELECTROLYSIS :
First Law :
w = zq w = Z it     Z = Electrochemical equivalent of substance
Second Law :
W ? E
E
W
 = constant
..........
E
W
E
W
2
2
1
1
? ?
96500
factor efficiency current t i
E
W ? ?
?
.
Current efficiency = 
100
produced deposited/  mass  l Theoritica
produced deposited/  mass  actual
?
CONDITION FOR SIMULTANEOUS DEPOSITION OF Cu & Fe AT CATHODE
Cu / Cu
2 º E ?
2
0591 . 0
? log 
? 2
Cu
1
 = 
Fe / Fe
2 º E ? ? 
2
0591 . 0
 log 
? 2
Fe
1
Condition for the simultaneous deposition of Cu & Fe on cathode.
CONDUCTANCE :
? Conductance = 
ce tan sis Re
1
Page 4


  
  
     
 
      
   
     
              
       
  
   
 
 
   
         
            
ELECTROCHEMISTRY
ELECTRODE POTENTIAL
For any electrode ? oxidiation potential = ? Reduction potential
E
cell
 = R.P of cathode ? R.P of anode
E
cell
 = R.P. of cathode + O.P of anode
E
cell
 is always a +ve quantity & Anode will be electrode of low R.P
Eº
Cell
 = SRP of cathode ? SRP of anode.
? Greater the SRP value greater will be oxidising power.
GIBBS FREE ENERGY CHANGE :
?G = ? nFE
cell
?Gº = ? nFEº
cell
NERNST EQUATION : (Effect of concentration and temp on emf of cell)
?G = ?Gº + RT ?nQ (where Q is raection quotient)
?Gº = ? RT ?n K
eq
E
cell
 = Eº
cell
 ? 
nF
RT
 ?n Q
E
cell
 = Eº
cell
 ? Q log
nF
RT 303 . 2
  
E
cell
 = Eº
cell
 ? 
n
0591 . 0
 log Q [At 298 K]
At chemical equilibrium
?G = 0 ; E
cell
 = 0.
? log K
eq
 = 
0591 . 0
E n
o
cell
.
Eº
cell
 =
n
0591 . 0
 log K
eq
For an electrode M(s)/M
n+
.
nF
RT 303 . 2
º E E
M / M M / M
n n ? ? ? ? log 
] M [
1
n?
.
CONCENTRATION CELL :
A cell in which both the electrods are made up of same material.
For all concentration cell Eº
cell
 = 0.
(a) Electrolyte Concentration Cell :
eg. Zn(s) / Zn
2+
 (c
1
) || Zn
2+
(c
2
) / Zn(s)
E = 
2
0591 . 0
 log 
1
2
C
C
(b) Electrode Concentration Cell :
eg. Pt, H
2
(P
1
 atm) / H
+
 (1M) / H
2
 (P
2
 atm) / Pt
E = 
2
0591 . 0
 log ?
?
?
?
?
?
?
?
2
1
P
P
DIFFERENT TYPES OF ELECTRODES :
1. Metal-Metal ion Electrode M(s)/M
n+
 . M
n+
 + ne
?
 ?? ? M(s)
E = Eº + 
n
0591 . 0
 log[M
n+
]
2. Gas-ion Electrode Pt /H
2
(Patm) /H
+
 (XM)
as a reduction electrode
H
+
(aq) + e
?
 ?? ?
2
1
H
2
 (Patm)
E = Eº ? 0.0591 log 
] H [
P 2
1
H
2
?
  
3. Oxidation-reduction Electrode Pt / Fe
2+
, Fe
3+
as a reduction electrode Fe
3+
 + e
?
 ?? ? Fe
2+
E = Eº ? 0.0591 log 
] Fe [
] Fe [
3
2
?
?
4. Metal-Metal insoluble salt Electrode eg. Ag/AgCl, Cl
?
as a reduction electrode  AgCl(s) + e
?
 ?? ? Ag(s) + Cl
?
Ag / AgCl / Cl
E ?
 = 
Ag / AgCl
0
/ Cl
E ?
 ? 0.0591 log [Cl
?
].
ELECTROLYSIS :
(a) K
+
, Ca
+2
, Na
+
, Mg
+2
, Al
+3
, Zn
+2
, Fe
+2
, H
+
, Cu
+2
, Ag
+
, Au
+3
.
 Increasing order of deposition.
(b) Similarly the anion which is strogner reducing agent(low value of SRP)
is liberated first at the anode.
diposition of order g sin Increa
, Br , Cl , OH , NO , SO
? ? ? ?
3
? 2
4
? ? ? ? ? ? ? ? ? ? ? ?
?
I
FARADAY?S LAW OF ELECTROLYSIS :
First Law :
w = zq w = Z it     Z = Electrochemical equivalent of substance
Second Law :
W ? E
E
W
 = constant
..........
E
W
E
W
2
2
1
1
? ?
96500
factor efficiency current t i
E
W ? ?
?
.
Current efficiency = 
100
produced deposited/  mass  l Theoritica
produced deposited/  mass  actual
?
CONDITION FOR SIMULTANEOUS DEPOSITION OF Cu & Fe AT CATHODE
Cu / Cu
2 º E ?
2
0591 . 0
? log 
? 2
Cu
1
 = 
Fe / Fe
2 º E ? ? 
2
0591 . 0
 log 
? 2
Fe
1
Condition for the simultaneous deposition of Cu & Fe on cathode.
CONDUCTANCE :
? Conductance = 
ce tan sis Re
1
  
? Specific conductance or conductivity :
(Reciprocal of specific resistance) K = 
?
1
K = specific conductance
? Equivalent conductance :
Normality
1000 K
E
?
? ?
unit : -ohm
?1
 cm
2
 eq
?1
? Molar conductance :
Molarity
1000 K
m
?
? ?
unit : -ohm
?1
 cm
2
 mole
?1
specific conductance = conductance × 
a
?
KOHLRAUSCH?S LAW :
Variation of ?
eq
 / ?
M
 of a solution with concentration :
(i) Strong electrolyte
?
M
c
 = 
?
?
M
 ? b
c
(ii) Weak electrolytes : ?
?
 = n
+
 ?
?
??
+ n
?
??
?
?
where ? is the molar conductivity
n
+
 = No of cations obtained after dissociation per formula unit
n
?
 = No of anions obtained after dissociation per formula unit
APPLICATION OF KOHLRAUSCH LAW :
1. Calculation of ?
0
M
 of weak electrolytes :
?
0
M
 
(CH3COOHl)
 = ?
0
M(CH3COONa)
 + ?
0
M(HCl) 
? ?
0
M(NaCl)
2. To calculate degree of diossociation of a week electrolyte
? = 
0
m
c
m
?
?
; K
eq
 = 
) 1 (
c
2
? ?
?
3. Solubility (S) of sparingly soluble salt & their K
sp
?
M
c
  = ?
M
?
   =   ? × 
ility lub so
1000
K
sp
 = S
2
.
Transport Number :
t
c
 = ?
?
?
?
?
?
? ? ?
?
a c
c
 , t
a
  = ?
?
?
?
?
?
? ? ?
?
c a
a
.
Where t
c
 = Transport Number of cation & t
a
 = Transport Number of
anion