If the concentration of the reactants is decreased by half while keeping the pressure and temperature constant, the reaction will shift towards the reactant side to restore the equilibrium. This is in accordance with Le Chatelier's principle, which states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust itself to counteract the change and re-establish a new equilibrium. In this case, by decreasing the concentration of reactants, the system will try to produce more reactants to compensate for the change and maintain the equilibrium constant.