Chemistry 9th Edition

Published by Cengage Learning
ISBN 10: 1133611095
ISBN 13: 978-1-13361-109-7

Chapter 18 - Electrochemistry - Review Questions - Page 875: 1


A half reaction is a component reaction of a redox reaction. The number of electrons lost in the oxidation process must equal the electrons gained in the reduction process in order to maintain law of conservation of charge. In order to balance reactions, half reactions should first be written separating the compounds. Each half reaction should then be balanced to account for elements involved, and then electrons should be utilized to balance charge differences. The two half reactions should then be combined and charges balanced. The reaction should be reviewed once more to ensure that all charges and elements are properly balanced. For any reaction, the number of elements on either side of the equation and the charge should always be balanced.

Work Step by Step

Redox reactions can be separated into two halves (thus half reaction), one reaction will be the oxidation half reaction where electrons are lost while the other reaction will be the reduction half reaction where electrons are gained. The law of conservation of charge dictates that the charge on both sides of a reaction should always be constant as charge can neither be created nor destroyed. Thus, the number of electrons which carry charge should always remain the same. The specific steps are detailed in the book. However, these rules apply for any reaction balancing that involves the transfer of electrons. The equation must be separated before it can be properly balanced utilizing both hydrogen and oxygen atoms to account for excess elements. All chemical reactions must obey the law of conservation of mass, mass cannot be created nor destroyed, thus the number of elements should be identical on both sides of the equation. The reaction must also obey the law of conservation of charge, charge cannot be created nor destroyed, thus the total charge on both sides of the reaction should be identical.
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