"Relationship
between Homogeneous Equilibrium and the Law of Mass Action (Part A)"
The Law of Mass Action is a fundamental principle that governs the equilibrium of a chemical reaction. It states that the rate of a chemical reaction is directly proportional to the product of the concentrations (or activities) of the reactants, each raised to the power of their respective coefficients in the balanced chemical equation. This law applies to both homogeneous and heterogeneous equilibria.
Case
A- In gaseous reaction where there are equal no of moles
In the case of homogeneous equilibrium,
the Law of Mass Action is expressed as:
H2
+ I2 ⇌ 2HI
t=0 a b 0
t=eq (a-x) (b-x) 2x
Suppose x is the amount of concentration
disappear at equilibrium position for reactants
Total no of moles “N” for this reaction
is (a-x)+ (b-x)+2x = (a+b)
Expression
for Kc:
[H2] = (a-x)/V
[I2] = (b-x)/V
[HI] = 2x/V
Put the values in Kc expression
Kc
= [HI]2
[H2][I2]
Kc
= [2x/V]2
[(a-x)/V][ (b-x)/V]
Kc = 4x2
(a-x)(b-x)
Expression for Kp:
According to Dalton theory,
pi = XiP we know that Xi = n/N
PH2
= (a-x) P
(a+b)
PI2
= (b-x) P
(a+b)
PHI
= (2x) P
(a+b)
Put the values in Kp expression
Kp
= PHI2
PH2 PI2
Kp
= PHI2
PH2 PI2
(2x)2 P
Kp = (a+b)
(a-x) P (b-x) P
(a+b) (a+b)
Kp = 4x2
(a-x)(b-x)
Expression for Kx:
XH2
= (a-x)
(a+b)
XI2
= (b-x)
(a+b)
XHI
= (2x)
(a+b)
Put the values in Kx expression
Kx
= XHI2
XH2 XI2
(2x)2
Kx = (a+b)
(a-x) (b-x)
(a+b) (a+b)
Kx = 4x2
(a-x)(b-x)
The results showed that Kc =
Kp = Kx
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