Can a system be at equilibrium if concentrations of reactants and products are unequal?

Yes, a system can be at equilibrium even if the concentrations of reactants and products are unequal.

In a chemical reaction, equilibrium does not necessarily mean that the concentrations of the reactants and products are equal. Rather, it refers to the point at which the rate of the forward reaction equals the rate of the reverse reaction. This is known as dynamic equilibrium. At this point, the concentrations of the reactants and products remain constant over time, but they are not necessarily equal.

The equilibrium constant, Kc, is used to express the relationship between the concentrations of the products and reactants at equilibrium. It is defined as the ratio of the concentrations of the products to the concentrations of the reactants, each raised to the power of their stoichiometric coefficients. If Kc is greater than 1, the equilibrium lies to the right, meaning there are more products than reactants at equilibrium. Conversely, if Kc is less than 1, the equilibrium lies to the left, meaning there are more reactants than products at equilibrium.

The Le Chatelier's principle also explains how a system at equilibrium responds to changes in concentration, temperature, or pressure. If a system at equilibrium is disturbed, it will adjust itself to counteract the change and restore equilibrium. For example, if the concentration of a reactant is increased, the system will shift to the right to consume the added reactant and produce more products, until a new equilibrium is established.

In conclusion, the concept of equilibrium in chemistry is not about having equal concentrations of reactants and products, but about achieving a state of balance where the rates of the forward and reverse reactions are equal. This balance can be achieved at different concentrations of reactants and products, depending on the nature of the reaction and the conditions under which it occurs.