Law of Mass Action-
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Law of Mass Action
Law of mass action was given by .
“At constt. temp, the rate of reacting substance is proportional to its active mass & rate of a chemical reaction is directly proportional to the product of the active masses of the reacting substances.
Rate of Reaction ∝ [A]
A+B <——-> C+D
Rate of reaction ∝ [A][B]
Applications of law of Mass Action-
Consider a homogeneous reaction which has attained equilibrium at particular temp.
A +B <——->C +D
[A],[B],[C] &[D] are the active masses of A,B,C,D, respectively
A/c to law of mass action-
Rate of forward reaction ∝ [A][B]
Rf= Kf[A][B]
Kf is velocity const. of forward reaction
Rate of back ward reaction ∝ [C][D]
Rb= Kb [C][D]
Kb= velocity constt. of back ward reacn
At equi.,
Rate of forward reaction= Rate of bakward reaction
Rf= Rb
Kf[A][B] = Kb[C][D]
Kf /Kb = [C][D] / [A][B]
Kf /Kb = Kc
here Kc=equilibrium constant
Kc= [C][D] / [A][B]
Suppose a reversible reaction at constant temp. is
aA+ bB <——> cC+ dD
[A]a, [B]b, [C]c, [D]d are the active masses of A , B , C & D respectively.
A/c to law of mass action,
Rate of forward reaction ∝ [A] a[B]b
Rf= Kf [A] a[B]b
Kf=velocity constant for forward reaction
Also
Rate of backward reaction ∝ [C]c[D]d
Rb= Kb [C] c[D]d
Kb= velocity constt. for back ward reaction
At equilibrium,
Rf=Rb
Kf [A] a[B]b =Kb [C] c[D]d
Kf /Kb =[C] c[D]d / [A] a[B]b
Kf /Kb = Kc
here Kc=equilibrium constant
Kc= [C] c[D]d / [A] a[B]b
