CHEMICAL EQUILIBRIUM-LAW OF MASS ACTION- EQUILIBRIUM CONSTANT


CHEMICAL EQUILIBRIUM


	ACTIVE MASS	www.citycollegiate.com
	Concentration of a substance expressed in mole/dm³ or in molar unit is called ACTIVE MASS. Active mass in mole/dm³ is represented by a square bracket [ ].
	LAW OF MASS ACTION
	According to the law of mass action.
	"The rate at which a substance reacts is directly proportional to its active mass "
	Rate µ [Reactant]
	The rate of reaction is directly proportional to the product of the active masses of reactants.
	Consider a general reversible reaction
	A + B C + D
	According to the law of mass action:
	Rate of reactionµ [A][B]
	Determination of equilibrium constant by using equilibrium law
	Consider a general reaction
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	aA + bB cC + dD
	According to the law of mass action
	Rate of forward reaction µ [A]^a[B]^b
	Rate of forward reaction = K_f [A]^a[B]^b
	Similarly,
	Rate of backward reaction µ [C]^c[D]^d
	Rate of backward reaction = K_b [C]^c[D]^d
	Where
	K_f = rate constant for forward reaction K_b = rate constant for backward reaction a, b, c, d = number of moles
	At equilibrium rate of forward reaction becomes equal to the rate of backward reaction, thus,
	Rate of forward reaction = Rate of backward reaction K_f [A]^a[B]^b = K_b [C]^c[D]^d K_f / K_b =[C]^c[D]^d/[A]^a[B]^b
	Let K_f/K_b = K_c
	K_c = [C]^c[D]^d/[A]^a[B]^b
	This is the expression of equilibrium constant where c represents concentration.
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