catalysis: the process by which a catalyst changes the rate and mechanism of a chemical reaction -- a catalyst is… NOT consumed during the course of a reaction -- Catalyzed and uncatalyzed reactions have... completely different mechanisms. This is WHY catalyzed and uncatalyzed reactions have different activation energies.

Homogeneous catalysts are present in the same phase as the reacting molecules. Heterogeneous catalysts exist in a different phase than the reacting molecules. -- usually solid catalysts in gaseous mixtures or liquid solutions Catalytic converters often use Pt as a catalyst to help turn CO into CO2, NxOx into N2 and O2, and unburned hydrocarbons into CO2 and H2O. Research on catalysts is one of the most important areas of modern science.

The first step in heterogeneous catalysis is _________ of the reactant molecules onto the metal surface – specifically, onto the _________, which are the locations at which reactants attach to the metal catalyst. adsorption active sites -- R bonds are broken or weakened, allowing P to form w/a lower Ea -- then, the products detach from the catalyst enzymes: biological catalysts -- large protein molecules (104 – 106 amu) -- usually very specific  for only one reaction -- names end in... “____” -ase -- substrates: substances (i.e., reactants) that react at the active sites of enzymes

-- The lock-and-key model explains how an enzyme affects a substrate molecule and changes it into a new substance. substrate (i.e., reactant) Lock-and-Key Model active site enzyme-substrate complex products enzyme active site is ready for more substrate

turnover number: ~103 – 107 per sec. Enzyme inhibitors bind to the active site or alter the unique shape of an enzyme molecule, destroying the enzyme’s activity. e.g., poisons, Pb, Hg, others