Empirical Effect of Catalysis Catalysis deals with the properties & development of catalysts, & the effects of catalysts on chemical reactions. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the overall process. Chlorophyll is a catalyst for photosynthesis. The inside of a catalytic converter in a car exhaust system is coated with an alloy that acts as a catalyst for the combustion of exhaust gases.

Theoretical Explanation of Catalysis A catalyst lowers the activation energy for a reaction. This results in a larger number of effective collisions between entities, so the reaction rate increases. The rate of the forward reaction & of the reverse reaction increases by the same amount. However, the net enthalpy for a reaction does not change.

Biological catalysts (enzymes) have binding sites specific to the reactants (substrate). The enzyme temporarily binds the substrate molecules and aligns them in the proper orientation. Note that enzyme shape does not change.

The uncatalyzed reaction proceeds slowly at room temperature.

The catalyzed reaction has a lower activation energy, thus having an increased rate.

A reaction mechanism describes the individual reaction steps and the intermediates formed during the reaction, starting with the reactants and finishing with the products. Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in a reaction mechanism.

Technologies such as spectrometers can show the intermediates that are formed. Spectrographs indicate that the chemical formulas for the intermediates of catalyzed decomposition of methanoic acid are HCOOH2+(aq) and HCO+(aq). It also shows that the products are H2O(l) and CO(g).

Example Step 1: reactant(s) → activated complex 1 → intermediate 1 Step 2: intermediate 1 → activated complex 2 → intermediate 2 Step 3: intermediate 2 → activated complex 3 → product(s)

Uses of Catalysts The Oil Industry Catalysts are used in the cracking and reforming of crude oil which reduces the temperature required for these processes, making them more efficient.

Upgrading of Bitumen from Oil Sands

Emissions Control

Enzymes

Homework: Read pgs. 535 – 541 pg. 542 Section 12.3 Questions #’s 1 – 6