Page 383 - Elements of Chemical Reaction Engineering Ebook

354 Nonelementary Reaction Kinetics Chap. 7

TABLE 7-2. STEPS TO DEDUCE A RATE LAW

1. Assume an activated intermediate(s).
2. Postulate a mechanism, utilizing the rate law obtained from experimental data, if possible.
3. Model each reaction in the mechanism sequence as an elementary reaction.
4. After writing rate laws for the rate of formation of desired product, write the rate laws for each
Once the rate law
is found, the search of the active intermediates.
for the mechanism 5. the PSSH.
begins 6. Eliminate the concentration of the intermediate species in the rate laws by solving the simul-
taneous equations developed in steps 4 and 5.
7. If the derived rate law does not agree with experimental observation, assume a new mechanism
and/or intermediates and go to step 3. A strong background in organic and inorganic chemistry
is helpful in predicting the activated intermediates for the reaction under consideration.

7.3 Polymerization

Polymers are finding increasing use throughout our society. Well over 100 bil-
lion pounds of polymer are produced each year and it is expected that this figure
lo1' Ibb/yr will double in the coming years as higher-strength plastics and composite mate-
rials replace metals in automobiles and other products. Consequently, the field
of polymerization reaction engineering will have an even more prominent place
in the chemical engineering profession. Since there are entire books on this field
(see Supplementary Reading) it is the intention here to give only the most rudi-
mentary thumbnail sketch of some of the principles of polymerization.
A polymer is a molecule made up of repeating structural (monomer)
units. For example, polyethylene, which is used for such things as tubing, and
electrical insulation is made up of repeating units of ethylene

where n may be 25,000 or higher.