aboratory: Chemical Equilibrium and Le Chatelier’s PrincipleL ......................................
Laboratory:
Chemical Equilibrium
and Le Chatelier’s Principle
In a chemical reaction, chemical equilibrium is the state in which the concentrations
of the reactants and products exhibit no net change over time. This state occurs when
the forward reaction rate (conversion of reactants to products) is equal to the reverse
reaction rate (conversion of products to reactants). These reaction rates are generally
greater than zero, but because the rates are equal, reactants are converted to products
at the same rate that products are converted to reactants, yielding zero net change in the
concentrations of reactants and products. A system in this state is said to have achieved
dynamic chemical equilibrium.The equilibrium is referred to as “dynamic” because any change to the reaction
environment in concentrations, temperature, volume, or pressure forces a corresponding
change in the equilibrium state. For example, if a chemical reaction has achieved dynamic
equilibrium and you add reactants, the state of the system changes to achieve a new
dynamic equilibrium. Some (but not all) of the additional reactants react to form additional
products, changing the concentrations of both the reactants and the products. Similarly, if
you remove products from the reaction vessel, the dynamic equilibrium changes because
additional reactants are converted to products.The nineteenth-century French chemist Henry Louis Le Chatelier explained the effect
of environmental changes on dynamic chemical equilibrium in a short statement that is
known to every chemist as Le Chatelier’s Principle:“If a chemical system that has achieved dynamic chemical equilibrium experiences an
imposed change in concentration, temperature, volume, or pressure, the equilibrium state
shifts to counteract, insofar as is possible, that imposed change.”