Question

Explain what is wrong with the following statement about chemical equilibrium:
The equilibrium constant always increases when the temperature in increased.

Answer 1

If a forward reaction is exothermic, increasing the temperature decreases the value of the equilibrium constant. If the forward reaction is endothermic, increasing the temperature increases the value of the equilibrium constant.

If you consider Le Chatelier's principle, you can explain those mechanisms. For an exothermic reaction, if the temperature increases, the reaction will shift to the left and so the concentration of product to reactant ratio will decrease, making Kc decrease. On the other hand, for an endothermic reaction, increasing the temperature provides more energy for the forward reaction and so the product to reactant ratio will increase, thus increasing Kc.