The type of reaction that occurs can further describe a chemical reaction.
There are three types of chemical reactions:- Synthesisreaction: Two or more atoms, ions, or molecules are bound to form
a larger molecule. A synthesis reaction combines substances called reactants
to form a new molecule, which is called a product. Areactantis a substance
that reacts in a reaction and the productis the result of a reaction. In Na++
Cl−→NaCl, sodium and chlorine are reactants and sodium chloride is the
product of this reaction. A synthesis reaction in a living organism is referred
to as an anabolic reactionor anabolism. These are metabolic pathways. - Decompositionreaction: A reaction that breaks the bond between atoms in a
molecule or chemical compound. In NaCl →Na++Cl−, sodium chloride is
broken up into its chemical elements sodium and chlorine. A decomposition
reaction in a living organism is called a catabolic reactionor catabolism. - Exchange reaction: A reaction that is both a synthesis reaction and a
decomposition reaction, where a chemical compound is decomposed into
its chemical elements and those chemical elements are synthesized into a
new chemical compound. In NaOH +HCl →NaCl +H 2 O, sodium hydrox-
ide (NaOH) and hydrochloric acid (HCl) enter into an exchange reaction
to form salt (NaCL) and water (H 2 O).
A chemical reaction theoretically can be reversed, but in practice some reac-
tions create an unstable chemical compound that might require special con-
ditions to exist for the reverse reaction to happen. Those special conditions
required to reverse a reaction appear below the arrow in the reaction notation.
Above the arrow appears any special condition that must exist for the synthe-
sized reaction to occur. In Fig. 2-6, a temperature of 250° C is the special con-
dition for the synthesized reaction to occur and absolute zero is necessary for the
decomposition reaction to occur.
Acatalyst is a substance that speeds up the rate of a chemical reaction by
decreasing the energy needed to run the reaction without changing the reactants
or products. Enzymes are an example of a biological substance that acts as cat-
alysts to speed up a reactor rate.
(^34) CHAPTER 2 Chemical Elements of Microorganisms
Fig. 2-6. In theory all chemical reactions are reversible. In
practice these are called reversible reactions.
XY+ XY
heat
water