Chemqueries: Important relationship involving equilibrium constants

Important relationship involving equilibrium constants

1. If we reverse an equation  KP or  KC  is reversed.
           If              A + B ⇔ C + D         KC = 10  
           then for    C + D  A + B          K= 10-1
    2. If we multiply each of the coefficient in a balanced equation by a factor n,then equilibrium constant is raised to the same factor.
      ½ N2 + ½O⇔ NO            KC = 5
                  N2  +  O⇔ 2NO               KC = 52 = 25 
     3. If we divide each of the coefficient in a balanced equation by a factor n,then new equilibrium constant is nth root of the previous value.
              2SO2 + O2      2SO3              KC =25
              SO2 + 1/2 O2   SO3B     KC = (25)1/2

    4. When we combine individual equation,we have to multiply their equilibrium constant for net     reaction.
               If KK2 and K are stepwise equilibrium constant for  A⇔B , B⇔C , C⇔D   .
              Then for A⇔D , equilibrium constant is K= K1K2K

    Significance of the magnitude of equilibrium constant:

    1. If a large value of KP or  KC signifies that the forward reaction goes to completion or very nearly so.
    2. A large value of KP or KC signifies that the forward reaction doesnot occur to any significiant extent.
    3. A reaction is most likely to reach a state of equilibrium in which both reactant and product are present if the numerical value of KP or  KC is neither very large nor very small

    Units of equilibrium constant:

               For the shake of simplicity in the units of Kc or Kp the relative molarity of pressure of  reactants and products are used with respect to standard condition.(For solution standard state 1 mol/litre and for gas standard pressure=1 atm).Now resulting equilibrium constant becomes unitless by using relative molarity and pressure.But the numerical value may change in the value of standard states molarity and pressure.

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