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

Asked by Khushbu Bisht(ANDHRA EDUCATION SOCIETY) , on 15/1/13

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 â†” cC + dD

Qc defined as

Qc= [D]d[C]c

[A]a[B]b

Posted by Sumeet Malikon 16/1/13

This conversation is already closed by Expert

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.

Posted by Saurabh Ranjanon 15/1/13

• 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.

Posted by Saurabh Ranjanon 15/1/13

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.

Posted by Saurabh Ranjanon 15/1/13

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

thubs up plzz!

Posted by Md Junaid(The Academy, Gallifrey) on 15/1/13

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!

Posted by Md Junaid(The Academy, Gallifrey) on 15/1/13