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Khushbu Bisht from ANDHRA EDUCATION SOCIETY, asked a question
Subject: Chemistry , asked on 15/1/13

 what is the difference between Qc and Kc and how it will calculate both?

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Sumeet Malik , Meritnation Expert added an answer, on 16/1/13

Reaction quotient is used to determine relative amounts of reactants and products at a particular point of time in the reaction where as equilibrium describes the same thing at equilibrium. Thus, the value of Q and k is s

For the reaction,

aA + bB ↔ cC + dD

Qc defined as

Qc= [D]d[C]c

  [A]a[B]b

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Saurabh Ranjan From Kendriya Vidyalaya, added an answer, on 15/1/13
16 helpful votes in Chemistry

For a general reaction,

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Md Junaid From The Academy, Gallifrey, added an answer, on 15/1/13
89 helpful votes in Chemistry

 K c   is ratio of rate constant of forward and backward reaction at equilibrium while Q c   is the ratio of rate constant of forward and backward reaction before coming to equilibrium or after equilibrium. Q c   becomes equal to K c   when rate of forward and backward reaction becomes equal.
 

thubs up plzz!

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Md Junaid From The Academy, Gallifrey, added an answer, on 15/1/13
89 helpful votes in Chemistry

 Reaction Quotient Q c - It is the function of the activities or concentrations of the species involved in a chemical reaction.

For a general reaction,

 

Thus it is the ratio of product of concentrations of the products and product of concentrations reactants, each concentration raised to the power equal to stoichiometric coefficient in the balanced equation at any stage of reaction.


Equilibrium constant K c- The ratio of product of concentrations of the products and product of concentration reactants, each concentration raised to the power equal to stoichiometric coefficient in the balanced equation at only equilibrium stage of reaction.

 

Reaction Quotient Q c pridicts the direction of reaction.

When Q K c : Reaction proceeds in forward direction

Q c > K c : Reaction proceeds in backward direction

Q K c : Reaction is in equilibrium


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Saurabh Ranjan From Kendriya Vidyalaya, added an answer, on 15/1/13
16 helpful votes in Chemistry

Mathematically the same equation  (1) is used for calculation Kc also. If we apply equation (1) to the reaction when it is already in equilibrium, it will give Kc but if we apply the same equation (1) at the time when reaction is not in equilibrium stage it will give the value of Qc. At equilibrium Qc becomes Kc.

 


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Saurabh Ranjan From Kendriya Vidyalaya, added an answer, on 15/1/13
16 helpful votes in Chemistry

Kc is equilibrium constant , it is used for predicting the extent of a reaction.

 

Qc is reaction quotient, is is used for predicting the direction of a reaction.

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Saurabh Ranjan From Kendriya Vidyalaya, added an answer, on 15/1/13
16 helpful votes in Chemistry
  • If Q C > K C , then the reaction will proceed in the reverse direction.
  • If Q C < K C , then the reaction will proceed in the forward direction.
  • If Q C = K C , then the reaction is at equilibrium.
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