230 DIY Science: Illustrated Guide to Home Chemistry Experiments
EvdRE y Ay CHEmICAL EqUILIBRIUm
The importance of chemical equilibrium and Le Chatelier’s Principle isn’t limited to chemistry labs.
These concepts are important in everyday life, including at least one application that we literally couldn’t live without.
Here are just a few of them.
- Human blood is a complex chemical system that is constantly in a finely balanced equilibrium. As you burn calories,
your cells produce carbon dioxide, which enters your bloodstream, forming carbonic acid and lowering the pH.
Biological pH meters located in your carotid artery, called carotid bodies, detect the lowered pH and cause you to
breathe faster. As the blood circulates through your lungs, it is exposed through the permeable membranes that
make up your lungs’ alveoli to atmospheric air, which contains less carbon dioxide. Carbon dioxide migrates from
the bloodstream to the outside air. By Le Chatelier’s Principle, the equilibrium shifts to the left. The concentration of
carbonic acid in your blood is reduced, and its pH returns to its normal level of about 7.4. - Hundreds of industrial chemicals used in thousands of everyday products from plastics to drugs, gasoline, and
coffee are produced in continuous-mode processes that depend upon chemical equilibrium. In these processes,
products are continuously removed from the reaction vessel to force the reaction to the right, giving higher yields
of the desired products. - Carbonated beverages are a perfect illustration of Le Chatelier’s Principle. These beverages are bottled under carbon
dioxide gas at high pressure to ensure that they’ll still be fizzy when you open them. Under high pressure, the carbon
dioxide gas reacts with water to form carbonic acid, as illustrated by the equilibrium equation: CO 2 + H 2 O ⇔ H 2 CO 3.
When you remove that pressure by opening the bottle or can, the equilibrium shifts to the left, converting the carbonic
acid back into water and carbon dioxide gas.
It’s important to understand two things about Le Chatelier’s
Principle. First, the equilibrium change can (almost) never return
the system to its original equilibrium state. For example, if you
add reactants to a system that has achieved dynamic chemical
equilibrium, the concentration of reactants at the new equilibrium
state will be higher than it was at the original equilibrium state
(although lower than it would have been without the change in
equilibrium state). Second, Le Chatelier’s Principle is qualitative,
rather than quantitative. That is, applying Le Chatelier’s Principle
tells you whether the reaction will be forced to the left (more
reactants) or to the right (more products), but it cannot tell
you how far the reaction will be forced or what the eventual
concentrations of reactants and products will be.
In this chapter, we’ll examine chemical reactions and Le
Chatelier’s Principle.