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Electrochemistry II: Balancing Equations
SOME GENERAL GUIDELINES
It should be evident that with a little practice you can very quickly, efficiently,
and infallibly balance the most complicated electron-transfer equations. It is a
straightforward mechanical process. This statement is true IF you know what
the products of oxidation and reduction are. The most difficult situation that
exists for balancing equations is the one characterized by the following request:
"Write a balanced ionic equation for the reaction, if any, that occurs when you
mix A and B." You know the potential reactants because they are given, but
that is all.
If you are faced with such a request, there is one question that must be
answered before any other: "Will it be an electron-transfer reaction?" The
answer depends on two basic requirements for an electron-transfer reaction.
1. The reactants must include both an oxidizing and a reducing agent.
2. In terms of Table 17-1, the reducing agent (on the righthand side of the
half-reaction) must \ieabove the oxidizing agent (on the lefthand side of
the half-reaction).
If both of these requirements are met, the reaction will be electron-transfer, and
the equation will be balanced by the principles outlined in this chapter. If only
one (or neither) of these requirements is met, the reaction (if any) will be limited
to such reactions as double decomposition, association, or dissociation as described in Chapter 27.
Lacking a table of standard electrode potentials, or one that is adequate,
what guidelines can be used to identify oxidizing and reducing agents, and to
estimate their relative strengths? Here are a few.
1. If uncombined elements are among the reactants, an electron-transfer
reaction is the only possibility. Metals can react only as reducing
agents; nonmetallic elements only as oxidizing agents.
2. If a reactant is an -ous acid, an -ite ion, or an -ous metal ion, there is
implied the existence of a higher valence form and thus the possibility
that the reactant is a reducing agent.
3. If a reactant is an -ic metal ion, there is implied the existence of a lower
valence form and thus the possibility that the reactant is an oxidizing
agent.
4. If the reactants include substances that are well-known strong oxidizing and reducing agents, then the reaction will be an electron-transfer
reaction.
Electrochemistry II: Balancing Equations
SOME GENERAL GUIDELINES
It should be evident that with a little practice you can very quickly, efficiently,
and infallibly balance the most complicated electron-transfer equations. It is a
straightforward mechanical process. This statement is true IF you know what
the products of oxidation and reduction are. The most difficult situation that
exists for balancing equations is the one characterized by the following request:
"Write a balanced ionic equation for the reaction, if any, that occurs when you
mix A and B." You know the potential reactants because they are given, but
that is all.
If you are faced with such a request, there is one question that must be
answered before any other: "Will it be an electron-transfer reaction?" The
answer depends on two basic requirements for an electron-transfer reaction.
1. The reactants must include both an oxidizing and a reducing agent.
2. In terms of Table 17-1, the reducing agent (on the righthand side of the
half-reaction) must \ieabove the oxidizing agent (on the lefthand side of
the half-reaction).
If both of these requirements are met, the reaction will be electron-transfer, and
the equation will be balanced by the principles outlined in this chapter. If only
one (or neither) of these requirements is met, the reaction (if any) will be limited
to such reactions as double decomposition, association, or dissociation as described in Chapter 27.
Lacking a table of standard electrode potentials, or one that is adequate,
what guidelines can be used to identify oxidizing and reducing agents, and to
estimate their relative strengths? Here are a few.
1. If uncombined elements are among the reactants, an electron-transfer
reaction is the only possibility. Metals can react only as reducing
agents; nonmetallic elements only as oxidizing agents.
2. If a reactant is an -ous acid, an -ite ion, or an -ous metal ion, there is
implied the existence of a higher valence form and thus the possibility
that the reactant is a reducing agent.
3. If a reactant is an -ic metal ion, there is implied the existence of a lower
valence form and thus the possibility that the reactant is an oxidizing
agent.
4. If the reactants include substances that are well-known strong oxidizing and reducing agents, then the reaction will be an electron-transfer
reaction.