Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
193
Redox Reactions
Redox Reactions
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
19
19.1 Oxidation and Reduction
A chemical reaction in which electrons are transferred from one
atom to another is called an oxidation–reduction reaction, or
redox reaction. For example, a thin sliver of zinc metal can be
burned to form zinc oxide.
Complete chemical equation: 2Zn(s) ϩ O 2 (g) 0 2ZnO(s)
Net ionic equation: 2Zn(s) ϩ O 2 (g) 0 2Zn 2ϩ ϩ 2O 2Ϫ (ions in crystal)
In this reaction, each zinc atom transfers two electrons to an oxygen
atom. The zinc atoms become Zn 2ϩ ions, while the oxygen atoms
become O 2Ϫ ions.
In a redox reaction, the loss of electrons from atoms of a substance is called oxidation, whereas the gain of electrons is called
reduction. In the reaction shown above, zinc loses electrons and is
therefore oxidized. Oxygen gains electrons and is therefore reduced.
You learned in previous chapters that the oxidation number of an
atom in an ionic compound equals the number of electrons lost or
gained by the atom when it forms an ion. Oxidation increases an
atom’s oxidation number; reduction decreases the oxidation number.
In zinc oxide, the oxidation number of zinc is ϩ2, and the oxidation
number of oxygen is Ϫ2. Note that oxidation numbers are written
with the positive or negative sign before the number (ϩ2, Ϫ2). Ionic
charge is written with the sign after the number (2ϩ, 2Ϫ).
Oxidation and reduction are complementary processes that
always occur together. The substance that is reduced in a redox reaction is called the oxidizing agent. The substance that is oxidized is
called the reducing agent. In the formation of zinc oxide, oxygen is
the oxidizing agent and zinc is the reducing agent.
Redox reactions are not limited to reactions in which atoms
change to ions or vice versa. For example, consider the synthesis of
hydrogen chloride gas from its elements.
H 2 (g) ϩ Cl 2 (g) 0 2HCl(g)
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
193
Redox Reactions
Redox Reactions
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
19
19.1 Oxidation and Reduction
A chemical reaction in which electrons are transferred from one
atom to another is called an oxidation–reduction reaction, or
redox reaction. For example, a thin sliver of zinc metal can be
burned to form zinc oxide.
Complete chemical equation: 2Zn(s) ϩ O 2 (g) 0 2ZnO(s)
Net ionic equation: 2Zn(s) ϩ O 2 (g) 0 2Zn 2ϩ ϩ 2O 2Ϫ (ions in crystal)
In this reaction, each zinc atom transfers two electrons to an oxygen
atom. The zinc atoms become Zn 2ϩ ions, while the oxygen atoms
become O 2Ϫ ions.
In a redox reaction, the loss of electrons from atoms of a substance is called oxidation, whereas the gain of electrons is called
reduction. In the reaction shown above, zinc loses electrons and is
therefore oxidized. Oxygen gains electrons and is therefore reduced.
You learned in previous chapters that the oxidation number of an
atom in an ionic compound equals the number of electrons lost or
gained by the atom when it forms an ion. Oxidation increases an
atom’s oxidation number; reduction decreases the oxidation number.
In zinc oxide, the oxidation number of zinc is ϩ2, and the oxidation
number of oxygen is Ϫ2. Note that oxidation numbers are written
with the positive or negative sign before the number (ϩ2, Ϫ2). Ionic
charge is written with the sign after the number (2ϩ, 2Ϫ).
Oxidation and reduction are complementary processes that
always occur together. The substance that is reduced in a redox reaction is called the oxidizing agent. The substance that is oxidized is
called the reducing agent. In the formation of zinc oxide, oxygen is
the oxidizing agent and zinc is the reducing agent.
Redox reactions are not limited to reactions in which atoms
change to ions or vice versa. For example, consider the synthesis of
hydrogen chloride gas from its elements.
H 2 (g) ϩ Cl 2 (g) 0 2HCl(g)