Fundamental Chemistry and Hydraulics - Mathematics and Statistics for the Environment - page 361

DID YOU KNOW?
The term chelate was first applied in 1920 by Sir Gilbert T. Morgan and H.D.K Drew (1920),
who stated: “The adjective chelate, derived from the great claw or chela ( chely —Greek) of
the lobster or other crustaceans, is suggested for the caliperlike groups which function as two
associating units and fasten to the central atom so as to produce heterocyclic rings.”
DID YOU KNOW?
A common free radical reaction in aqueous solution is electron transfer , especially to the
hydroxyl radical and to ozone.
• Photolysis ( photo , light; lysis , to break) is generally a decomposition reaction in which the
adsorption of light produces a photochemical reaction. Photolysis reactions form free radi-
cals that can undergo other reactions. For example, the chlorine molecule can dissociate in
the presence of high-energy light (for example, ultraviolet light).
Cl 2 + UV Energy ⇒ Cl - + Cl -
Key Point: Photolysis is an important nonthermal technology used for treating dioxin and furan
hazardous wastes.
• Polymerization is a combination reaction in which small organic molecules are linked
together to form long chains, or complex two- and three-dimensional networks.
Polymerization occurs only in molecules having double or triple bonds and is usually
dependent on temperature, pressure, and a suitable catalyst. Free radical chain reactions are
a common mode of polymerization. The term “chain reaction” is used because each reac-
tion produces another reactive species (i.e., another free radical) to continue the process.
Note: Catalysts are agents that change the speed of a chemical reaction without affecting the yield
or undergoing permanent chemical change.
Key Point: Plastics are perhaps the most common polymers, but there are also many important
biopolymers such as polysaccharides.
• Biochemical reactions are reactions that occur in living organisms.
• Biodegradation is a decomposition reaction that occurs in microorganisms to create
smaller, less complex inorganic and organic molecules. Usually the products of biodegra-
dation are molecular forms that tend to occur in nature.
14.1.2.9.3 Reaction Rates (Kinetics)
The rate of a chemical reaction is a measure of how fast the reaction proceeds—that is, how fast
reactants are consumed and products are formed.
A + B (reactants) ⇒ C + D (products)
The rate of a given reaction depends on many variables, including temperature, concentration of
the reactants, catalysts, structure of the reactants, and the pressure of gaseous reactants or products.
Without considering extreme conditions, in general reaction rates increase due to the following: