Final answer:
Chemical equilibrium occurs when a reversible process reaches a state where forward and reverse reaction rates are equal, resulting in no net change in reactant and product concentrations. It can be disturbed by changing conditions, causing shifts in the system as predicted by Le Chatelier's Principle. The equilibrium constant, K, and reaction quotient, Q, mathematically define the system's composition at and approaching equilibrium.
Step-by-step explanation:
Understanding Chemical Equilibrium
Chemical equilibrium is a state in a reversible chemical or physical process where the rate of the forward reaction equals the rate of the reverse reaction. In a system at equilibrium, the amounts of reactants and products remain constant over time, though the individual molecules may be constantly reacting. This state can be represented by a set of double arrows, indicating that the reactions are ongoing in both directions.
Experimental observations of equilibrium might include the constant color of a solution, the unchanging pressure in a closed container of gases, or steady temperature in an exothermic or endothermic process. These observable traits imply that, on a macroscopic level, there is no net change in the system.
According to Le Chatelier's Principle, the system can be 'stressed' by changes in conditions such as concentration, temperature, or pressure. This causes the equilibrium to shift in a direction that reduces the stress, meaning that the system will adjust to minimize changes and re-establish a new equilibrium state.
The equilibrium constant, K, and the reaction quotient, Q, are mathematical expressions representing the composition of a reaction at equilibrium and at any moment, respectively. When Q = K, the reaction is at equilibrium. If Q doesn't equal K, the system will shift its equilibrium position to reduce the difference, moving Q towards K.