The reaction in the question is that for the formation of ammonia. The arrow in the reaction should be a reversible arrow. Because of the negative ΔH value, the forward reaction is exothermic while the reverse reaction is endothermic.
An increase in temperature of a system at equilibrium favors the endothermic reaction, hence the reverse reaction (the reactants) is favored. And when the reverse reaction is favored, more reactants are produced. Hence, product formation (at equilibrium) is not favored as the temperature is raised.
