What do square brackets indicate in a chemical equation?

Square brackets in a chemical equation indicate the concentration of a species in a solution, typically expressed in moles per liter (Molarity). This notation is commonly used in the context of chemical reactions, especially those occurring in solution, to provide clear information about the effective concentration of reactants or products involved in the reaction.

For example, in the equation [A] + [B] → [C], the concentrations of A and B indicate how much of each substance is present in the solution, affecting the rate of the reaction and the position of equilibrium if the reaction is reversible. Understanding the concentration is crucial because it directly influences the reaction dynamics and the extent to which products are formed.

This notation plays a significant role in various aspects of chemistry, including kinetics and equilibrium, where concentrations can determine the speed of a reaction or the balance between reactants and products.