What is one issue that prevents achieving a 100% yield in reversible reactions?

In reversible reactions, one key issue that prevents achieving a 100% yield is that the products can react to form new reactants. This occurs when the forward reaction produces products that can then react back into the reactants or even generate different compounds. Because the reaction can proceed in both directions, it creates a dynamic equilibrium where the concentrations of reactants and products remain constant but not necessarily at their maximum potential.

At equilibrium, the system does not favor the complete conversion of reactants into products, and this behavior is a fundamental characteristic of reversible reactions. Therefore, even if all the reactants were initially present, the existence of this backward reaction means that some amount of the products will always revert back to reactants, thus preventing a complete yield of products.

Other factors mentioned, such as reagent purity, unreacted excess, or suboptimal temperature, can contribute to yield limitations but do not capture the essence of why reversible reactions inherently struggle to achieve 100% yield as succinctly as the interplay of forward and backward reactions.