Final answer:
When a reactant is added to a chemical equilibrium, the system shifts in a way that decreases the concentrations of the other reactants and increases the concentration of the products in order to re-establish equilibrium with the same equilibrium constant (K).
Step-by-step explanation:
Adding a reactant will decrease the amounts of the other reactants and increase the amount of products until a new position of equilibrium is found that has the same K.
According to Le Chatelier's principle, if a reactant is added to a system at equilibrium, the system will adjust by shifting the equilibrium position to favor the formation of products, thereby using up the added reactant. This phenomenon helps the system to re-establish equilibrium. However, despite these changes in concentration, the equilibrium constant (K) remains unchanged because it is only dependent on temperature for a given reaction.
Addition of reactant causes the reaction quotient (Q) to be smaller than the equilibrium constant (K), prompting the forward reaction to proceed, which leads to decreased concentrations of the other reactants and increased concentrations of the products.