To maximize the yield of a desired product, what should be controlled in a chemical reaction?

Controlling the temperature and concentration of reactants is crucial in optimizing the yield of a desired product in a chemical reaction. Temperature influences the reaction kinetics; higher temperatures often increase the rate of reaction, allowing reactants to collide more effectively, which can lead to a higher yield. However, some reactions may also have an optimal temperature, above or below which the yield could decrease due to changes in the reaction mechanism or the formation of unwanted by-products.

Concentration plays a key role as well. According to Le Chatelier's principle, if the concentration of reactants is increased, the equilibrium position of the reaction may shift toward the formation of more products, thus increasing the yield. Conversely, decreasing the concentration of products can also drive the reaction toward more product formation.

Thus, managing these two factors—temperature and reactant concentration—can have a significant impact on the efficiency and yield of a desired product in a chemical reaction. The other options, while relevant in different contexts, do not directly address the fundamental principles that maximize product yield effectively.