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What is equilibrium? The word "equilibrium"
describes the reaction conditions where, at the same time reactants
are forming products in the "forward" direction, the products
undergo a chemical change to form reactants in the "reverse"
direction. At equilibrium, the rate of the forward reaction is equal
to the rate of the reverse reaction, and thus the interchange of
reactants and products is constant. The system is in a state of
balance, and even though both the forward and the reverse reaction
are occurring simultaneously, the concentrations of all substances
in the system remain constant.
The process of equilibrium governs many of the chemical
reactions taking place in the human body. Enzymes work this way.
An enzyme is a very, very large molecule in the body that works
as a catalyst - it lowers the energy barrier of a reaction so that
it can proceed at a faster rate. Without the enzyme, some reactions
of the human body might take up to one million years to spontaneously
occur! The enzyme's near impossible job of speeding up reactions
operates under the process of equilibrium.
In biochemical processes, the enzymes in our body catalyze both
the forward and reverse reactions they are designed to "speed
up". Therefore, our cells do not over-produce certain chemicals
and always have reactants to convert into products in the forward
direction when needed.
The behavior of any system at equilibrium, including
those catalyzed by enzymes in the body, obeys Le Chatlier's principle.
Le Chatlier's principle predicts that if a stress is applied to
a system at equilibrium, the system will adjust toward a new equilibrium
state in a direction that reduces the stress.
Today you will examine three equilibrium systems.
You will apply different "stresses" to each system, including
changing the temperature or the concentration of one of the substances
involved. You will predict, using Le Chatlier's principle, which
way the equilibrium will shift to accommodate the stress. Then,
after observing the change in the system, note whether Le Chatlier's
principle was obeyed.
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