Important Chemical Equilibrium Formulas for JEE and NEET

 Page 1


  
       
       
        
    
         
  
  
     
    
   
    
      
  
  
 
   
 
     
 
  
 
CHEMICAL EQUILIBRIUM
At equilibrium :
(i) Rate of forward reaction  = rate of backward reaction
(ii) Concentration (mole/litre) of reactant and product becomes constant.
(iii) ?G = 0.
(iv) Q = K
eq.
Equilibrium constant (K) :
K = 
reaction backward of t tan cons rate
reaction forward of t tan cons rate
 = 
b
f
K
K
.
Equilibrium constant in terms of concentration (K
C
) :
b
f
K
K
 = K
C
 = 
b a
d c
] B [ ] A [
] D [ ] C [
Equilibrium constant in terms of partial pressure (K
P
 ) :
K
P
 = 
b
B
a
A
d
D
c
C
] P [ ] P [
] P [ ] P [
Equilibrium constant in terms of mole fraction (K
x
) :
 K
x
 = 
b
B
a
A
d
D
c
C
x x
x x
Relation between K
p
 & K
C
 :
K
p
 = K
c
.(RT)
?n
.
Page 2


  
       
       
        
    
         
  
  
     
    
   
    
      
  
  
 
   
 
     
 
  
 
CHEMICAL EQUILIBRIUM
At equilibrium :
(i) Rate of forward reaction  = rate of backward reaction
(ii) Concentration (mole/litre) of reactant and product becomes constant.
(iii) ?G = 0.
(iv) Q = K
eq.
Equilibrium constant (K) :
K = 
reaction backward of t tan cons rate
reaction forward of t tan cons rate
 = 
b
f
K
K
.
Equilibrium constant in terms of concentration (K
C
) :
b
f
K
K
 = K
C
 = 
b a
d c
] B [ ] A [
] D [ ] C [
Equilibrium constant in terms of partial pressure (K
P
 ) :
K
P
 = 
b
B
a
A
d
D
c
C
] P [ ] P [
] P [ ] P [
Equilibrium constant in terms of mole fraction (K
x
) :
 K
x
 = 
b
B
a
A
d
D
c
C
x x
x x
Relation between K
p
 & K
C
 :
K
p
 = K
c
.(RT)
?n
.
  
Relation between K
p
 & K
X
 :
K
P 
 = K
x
 (P)
?n
* log 
1
2
K
K
 = 
R 303 . 2
H ?
?
?
?
?
?
?
?
2 1
T
1
T
1
 ; ?H = Enthalpy of reaction
Relation between equilibrium constant & standard free energy change :
?Gº = ? 2.303 RT log K
Reaction Quotient (Q) :
The values of expression Q = 
b a
d c
] B [ ] A [
] D [ ] C [
Degree of Dissociation (?) :
?  = no. of moles dissociated / initial no. of moles taken
     = fraction of moles dissociated out of 1 mole.
Note :?% dissociation = ? x 100
Observed molecular weight and Observed Vapour Density of the mixture :
Observed molecular weight of A
n
(g)
= 
molecular weightof equilibrium mixture
totalno.of moles
0
o T
M ) 1 n (
M M
d ) 1 n (
d D
?
?
?
? ?
?
? ?
External factor affecting equilibrium :
Le Chatelier's Principle:
If a system at equilibrium is subjected to a disturbance or stress that
changes any of the factors that determine the state of equilibrium, the
system will react in such a way as to minimize the effect of the
disturbance.
Effect of concentration :
* If the concentration of reactant is increased at equilibrium then reaction
shift in the forward direction .
* If the concentration of product is increased then equilibrium shifts in the
backward direction
Effect of volume :
* If volume is increased pressure decreases hence reaction will shift in the
direction in which pressure increases that is in the direction in which
number of moles of gases increases and vice versa.
* If volume is increased then, for
?n > 0 reaction will shift in the forward direction
?n < 0 reaction will shift in the backward direction
?n = 0 reaction will not shift.
Page 3


  
       
       
        
    
         
  
  
     
    
   
    
      
  
  
 
   
 
     
 
  
 
CHEMICAL EQUILIBRIUM
At equilibrium :
(i) Rate of forward reaction  = rate of backward reaction
(ii) Concentration (mole/litre) of reactant and product becomes constant.
(iii) ?G = 0.
(iv) Q = K
eq.
Equilibrium constant (K) :
K = 
reaction backward of t tan cons rate
reaction forward of t tan cons rate
 = 
b
f
K
K
.
Equilibrium constant in terms of concentration (K
C
) :
b
f
K
K
 = K
C
 = 
b a
d c
] B [ ] A [
] D [ ] C [
Equilibrium constant in terms of partial pressure (K
P
 ) :
K
P
 = 
b
B
a
A
d
D
c
C
] P [ ] P [
] P [ ] P [
Equilibrium constant in terms of mole fraction (K
x
) :
 K
x
 = 
b
B
a
A
d
D
c
C
x x
x x
Relation between K
p
 & K
C
 :
K
p
 = K
c
.(RT)
?n
.
  
Relation between K
p
 & K
X
 :
K
P 
 = K
x
 (P)
?n
* log 
1
2
K
K
 = 
R 303 . 2
H ?
?
?
?
?
?
?
?
2 1
T
1
T
1
 ; ?H = Enthalpy of reaction
Relation between equilibrium constant & standard free energy change :
?Gº = ? 2.303 RT log K
Reaction Quotient (Q) :
The values of expression Q = 
b a
d c
] B [ ] A [
] D [ ] C [
Degree of Dissociation (?) :
?  = no. of moles dissociated / initial no. of moles taken
     = fraction of moles dissociated out of 1 mole.
Note :?% dissociation = ? x 100
Observed molecular weight and Observed Vapour Density of the mixture :
Observed molecular weight of A
n
(g)
= 
molecular weightof equilibrium mixture
totalno.of moles
0
o T
M ) 1 n (
M M
d ) 1 n (
d D
?
?
?
? ?
?
? ?
External factor affecting equilibrium :
Le Chatelier's Principle:
If a system at equilibrium is subjected to a disturbance or stress that
changes any of the factors that determine the state of equilibrium, the
system will react in such a way as to minimize the effect of the
disturbance.
Effect of concentration :
* If the concentration of reactant is increased at equilibrium then reaction
shift in the forward direction .
* If the concentration of product is increased then equilibrium shifts in the
backward direction
Effect of volume :
* If volume is increased pressure decreases hence reaction will shift in the
direction in which pressure increases that is in the direction in which
number of moles of gases increases and vice versa.
* If volume is increased then, for
?n > 0 reaction will shift in the forward direction
?n < 0 reaction will shift in the backward direction
?n = 0 reaction will not shift.
  
Effect of pressure :
If pressure is increased at equilibrium then reaction will try to decrease
the pressure, hence it will shift in the direction in which less no. of moles
of gases are formed.
Effect of inert gas addition :
(i) Constant pressure :
If inert gas is added then to maintain the pressure constant, volume
is increased. Hence equilibrium will shift in the direction in which larger
no. of moles of gas is formed
?n > 0 reaction will shift in the forward direction
?n < 0 reaction will shift in the backward direction
?n = 0 reaction will not shift.
(ii) Constant volume :
Inert gas addition has no effect at constant volume.
Effect of Temperature :
Equilibrium constant is only dependent upon the temperature.
If plot of ?nk vs 
T
1
 is plotted then it is a straight line with slope = ? 
R
H? ?
,
and intercept = 
R
S? ?
* For endothermic (?H > 0) reaction value of the equilibrium constant
increases with the rise in temperature
* For exothermic (?H < 0) reaction, value of the equilibrium constant
decreases with increase in temperature
* For ?H > 0, reaction shiffts in the forward direction with increase in
temperatutre
* For ?H < 0, reaction shifts in the backward direction with increases in
temperature.
* If the concentration of reactant is increased at equilibrium then reaction
shift in the forward direction .
* If the concentration of product is increased then equilibrium shifts in the
backward direction
Vapour Pressure of Liquid :
Relative Humidity = 
. temp that at O H of pressure Vapour
vapours O H of pressure Partial
2
2
Thermodynamics of Equilibrium :
?G = ?G
0 
+ 2.303 RT log
10
Q
Vant Hoff equation- log
?
?
?
?
?
?
?
?
2
1
K
K
 = 
R 303 . 2
H
0
?
 
?
?
?
?
?
?
?
?
?
1 2
T
1
T
1