Answer:
Causes the equilibrium to shift to the left, in favor of making more reactants, and K decreases.
Explanation:
Le Châtelier's principle states that if there is a stress in equilibrium, the reaction will shift to restore the equilibrium. An exothermic reaction loses heat for the surroundings, so the equilibrium must be represented as:
Reactants ⇔ Products + Heat
Then, when more heat is added, to restore the equilibrium, the reaction shift to the left ("consuming" heat), in favor of making more reactants.
The equilibrium constant (K) is:
K = [Products]/[Reactants]
So, [Reactants] will increase, and K must decrease.