Biomedical Engineering Reference
In-Depth Information
3.1. CHEMICAL SPECIES
We begin our study by performing mole balances on each chemical species in the
system. Here, the term chemical species refers to any chemical compound, element, or
living organism with a given identity. The identity of a chemical species is determined
by the kind, number,andconfiguration of that species' atoms. For example, the species
penicillin V (C
16
H
18
O
4
N
2
S, an antibiotic) is made up of a fixed number of specific
elements in a definite molecular arrangement or configuration. The structure shown illus-
trates the kind, number, and configuration of the species penicillin V on a molecular
level.
H
H
O
O
N
N
O
O
S
S
N
N
O
O
OH
OH
Penicillin V
Chemical species are commonly represented by elemental formula (NH
3
for ammonia, N
2
for nitrogen, H
2
O for water, C
16
H
18
O
4
N
2
S for penicillin V, and so on) and Roel's formula. Roel's
formula is elemental formula normalized by carbon (
Tabl e 3 .1
). For example, penicillin V
is represented by CH
1.125
O
0.25
N
0.125
S
0.0625
.
Even though two chemical compounds have exactly the same number of atoms of
each element, they could still be different species because of different configurations.
For example, glucose and fructose both have six carbon atoms, 12 hydrogen atoms,
and six oxygen atoms; however,
the atoms in the two compounds are arranged
differently.
As a consequence of the different configurations, these two isomers display different
chemical and physical properties. Therefore, we consider them as two different species
even though each has the same number of atoms of each element.
3.2. CHEMICAL REACTIONS
We say that a chemical reaction has taken place when a detectable number of molecules of
one or more species have assumed a new form by a change in the kind or number of atoms
in the compound and/or by a change in structure or configuration of these atoms. To
begin, let us look at one particular reaction in the production of soft drinks. Soft drinks
are essentially sweetened water with a small amount of flavoring added (usually
synthetic). The natural sugar
in sugarcane and sugar beets is primarily sucrose,
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