Effect of Temperature on Keq
Changing the temperature favours one reaction over the other. Therefore a shift in the Keq value is caused, as well as a change in the [participants]. A new equilibrium will be reached with it's own Keq value for the reaction at that temperature. At constant temperature, changing the equilibrium concentration does not affect Keq because the rate constants are not affected by the concentration changes.
When the concentration of one of the participants is changed, the concentration of the others vary in such a way as to maintain a constant value for the Keq.
Relationship of Keq to the Extent of Reaction
The magnitude of Keq is a measure of the extent to which a given reaction has or will take place.
A large value of Keq indicates that, at equilibrium there is a high concentration of products and a relatively low concentration of reactants.
A small value of Keq indicates that at equilibrium, the concentration of reactants is still high compared with that of the products.
A Keq value of 1 means that half of the reactants have turned into products. Therefore if the Keq is 1 then there should be a 50.0% yield.
If the Keq is about 1 x 1010 then the reaction has gone almost to completion.
If the Keq is about 1 x 10-10 it is essentially an incomplete reaction.
1.0 x 10-10                                                                 1                                                       1.0 x 1010
       |                                                           |                                                              |
0.0001%    1%                                                                   50%                                                                  99.9%    99.999%