If a reaction is exothermic and produces large quantities of heat reaching equilibrium, its equilibrium constant will be

The equilibrium constant will be lowered and the equilibrium will shift to the left if the heat being produced is not removed.

Explanation:

For an exothermic reaction, heat is actually a product of the reaction. to keep with Le Chatelier's principle, if the temperature is increased you're increasing the number of the product, and then you shift the balance at equilibrium back toward reactants, which means there'll be additional reactants left at equilibrium.

The equilibrium constant will be lowered and the equilibrium will shift to the left if the heat being produced is not removed.