What does the equation -(rA)/a = -(rB)/b = (rC)/c = (rD)/d represent in chemical reactions?

The equation -(rA)/a = -(rB)/b = (rC)/c = (rD)/d represents a fundamental concept in chemical kinetics, specifically the relationship between stoichiometry and the rate of reaction. This expression is derived from the law of stoichiometry, which relates the rate at which reactants are consumed to the rate at which products are formed, based on the coefficients in the balanced chemical equation.

In this equation:

• rA, rB, rC, and rD are the rates of change of the concentrations of species A, B, C, and D, respectively.
• a, b, c, and d are the stoichiometric coefficients from the balanced chemical equation.

The negative signs for the reactants (A and B) indicate that their concentration decreases as the reaction proceeds, while the positive signs for the products (C and D) indicate that their concentration increases. This equality signifies that the rates of consumption of reactants are proportional to their coefficients in the reaction, which in turn are proportional to the rates of formation of the products. Thus, this equation provides a clear relationship between stoichiometry and the reaction kinetics, allowing for the calculation of reaction rates and concentrations of reactants