In some cases, reactions occur so slowly that without a catalyst, they are of little value. Nearly all reactions that occur in living cells require catalysts called enzymes- without them, life would be impossible. Examples of homogeneous catalysis. Catalysts in solution with the reactants usually provide fast reaction paths by allowing reactants to form an unstable intermediate that quickly decomposes into products. The iodide-catalyzed decomposition of hydrogen peroxide is another classic example of homogenous catalysis.
Some enzymes contain embedded metal ions or other molecules that participate in the active site.
An example is carbonic anhydrase, which contains a zinc ion. The equilibrium lies far to the right, and rapid equilibration is essential to allow CO 2 to diffuse out of the bloodstream and into the lungs. Unlike most inorganic catalysts, enzymes are reaction specific. They act only on particular substrates, which fit into their convoluted surfaces like a key fits a keyhole. Also unlike most inorganic catalysts, enzymes are delicate, intricate molecular machines which can be damaged or destroyed by substances involved in the reaction they catalyze.