A method of controlling an exothermic or endothermic chemical reaction is provided. The method involves measuring a temperature of a first reactant flowing at a first flow rate, contacting the first reactant with a second reactant flowing at a second flow rate to form a reaction product, measuring the temperature of the reaction product, and determining the temperature difference between the temperature of the first reactant and the temperature of the reaction product. The method can further involve adjusting the flow rate of at least one of the first reactant and the second reactant, or shutting down flow, based on the temperature difference. An apparatus to carry out the method is also provided. The method and apparatus can be useful in controlling many different reactions, including the reaction of sodium hypochlorite and ammonia to form monochloramine.
