Balancing Oxidation-Reduction Reactions

This is an acid-base reaction in which a weak acid is used to produce an even weaker acid. Is it also an oxidation-reduction reaction Balance the equation. 

Balancing simple oxidation-reduction reactions by the half-reaction method Given an oxidation-reduction reaction, balance it. (EXAMPLE 4.8)... 

Oxidation-reduction reactions must be balanced if correct predictions are to be made. Just as in selecting a route for a trip from San Francisco to New York, there are several ways to reach the desired goal. Which route is best depends to some extent upon the likes and dislikes of the traveler. We will discuss two ways to balance oxidation-reduction reactions—first, using half-reactions and, next, using the oxidation numbers we have just introduced. 

Use of Half-Reactions for Balancing Oxidation-Reduction Reactions... 

Verify that reaction (23) is an oxidation-reduction reaction and that the oxidation number change of carbon is balanced by the oxidation number change of the sulfur. 

Bacteria, 434 Balancing reactions, 42 by half-reactions, 218 by oxidation number, 219 oxidation-reduction reactions, 217, 219... 

Oxidation-reduction reactions, 202 balancing with half-reactions, 217 balancing with oxidation numbers, 219 Oxides basic, 382... 

Balancing the chemical equation for a redox reaction by inspection can be a real challenge, especially for one taking place in aqueous solution, when water may participate and we must include HzO and either H+ or OH. In such cases, it is easier to simplify the equation by separating it into its reduction and oxidation half-reactions, balance the half-reactions separately, and then add them together to obtain the balanced equation for the overall reaction. When adding the equations for half-reactions, we match the number of electrons released by oxidation with the number used in reduction, because electrons are neither created nor destroyed in chemical reactions. The procedure is outlined in Toolbox 12.1 and illustrated in Examples 12.1 and 12.2. 

In Sec. 13.2 we will learn to determine oxidation numbers from the formulas of compounds and ions. We will learn how to assign oxidation numbers from electron dot diagrams and more quickly from a short set of rules. We use these oxidation numbers for naming the compounds or ions (Chap. 6 and Sec. 13.4) and to balance equations for oxidation-reduction reactions (Sec. 13.5). In Sec. 13.3 we will learn to predict oxidation numbers for the elements from their positions in the periodic table in order to be able to predict formulas for their compounds and ions. 

Determining the net ionic equation by balancing the oxidation-reduction reaction skeletal equation Cu(s) + HN03(ag) - Cu2+(aq) + NO(g)... 

The usefulness of determining the oxidation number in analytical chemistry is twofold. First, it will help determine if there was a change in oxidation number of a given element in a reaction. This always signals the occurrence of an oxidation-reduction reaction. Thus, it helps tell us whether a reaction is a redox reaction or some other reaction. Second, it will lead to the determination of the number of electrons involved, which will aid in balancing the equation. These latter points will be discussed in later sections. 

Material balances can be written for moieties which are conserved during the reaction, such as the atoms of a particular element or the total charge, or for reactant or product species if the stoichiometry is unambiguous. Oxidation-reduction reactions may be particularly troublesome. In the following situation, for example, one cannot write a material balance relating protons to water molecules. Consider the oxidation of O2 to H2O and the equilibrium dissociation of I O. 

In this chapter, you will be introduced to oxidation-reduction reactions, also called redox reactions. You will discover how to identify this type of reaction. You will also find out how to balance equations for a redox reaction. 

Many metals are also vulnerable to acids, undergoing an oxidation /reduction reaction that produces the metal ion and hydrogen gas. The balanced equation for the reaction between HCl and magnesium is... 

Balancing oxidation-reduction reactions is similar to balancing other types of reactions ... 

First, balance the number of atoms then, balance all of the transferred electrons. However, these simple rules are often difficult to apply in oxidation-reduction reactions (redox reactions). 

We can now construct a balance sheet for glycolysis to account for (1) the fate of the carbon skeleton of glucose, (2) the input of P, and ADP and the output of ATP, and (3) the pathway of electrons in the oxidation-reduction reactions. The left-hand side of the following equation shows all the inputs of ATP, NAD+, ADP, and Pj (consult Fig. 14-2), and the right-hand side shows all the outputs (keep in mind that each molecule of glucose yields two molecules of pyruvate) ... 

So we see that with the proper setup it is possible to harness electrical energy from an oxidation-reduction reaction. The apparatus shown in Figure 11.8 is one example. Such devices are called voltaic cells. Instead of two containers, a voltaic cell can be an all-in-one, self-contained unit, in which case it is called a battery. Batteries are either disposable or rechargeable, and here we explore some examples of each. Although the two types differ in design and composition, they function by the same principle two materials that oxidize and reduce each other are connected by a medium through which ions travel to balance an external flow of electrons. 

The reaction between sodium metal and water is shown in the Sodium and Potassium in Water movie eChapter 14.14). Write and balance the equation for this reaction. Is this an oxidation-reduction reaction If so, identify the oxidizing and reducing agents. 

There are two general approaches to balancing an oxidation-reduction reaction. Sometimes one is easier, sometimes the other, so it is best to master both. Both methods start with the same two steps ... 

The half-reaction method is a way of balancing oxidation-reductions reactions by the recognition of oxidation and reduction with separate reactions. Included in the reactions are the number of electrons that move and the nature of movement (gain or loss). The steps for this technique are ... 

Half-reactions can be added to produce a net reaction, which is the oxidation-reduction reaction. However, this summation cannot be performed unless the electron numbers are the same on both sides of the reaction by agreement among chemists, electrons are not written into summation reactions. The way in which adjustments are made is to preserve the ratio of coefficients in the individual balanced half-reaction by multiplying all of the participants in an equation by the same number. The goal is to have the same number of electrons on opposite sides of the half-reactions. The electrons will then algebraically cancel when the half-reactions are added. Since the summation equation should not have coefficients divisible by a common factor, it is customary to choose numbers that will yield the least number of electrons for cancellation. 

Master the half-reaction method before studying electrochemistry. The studies of electrochemistry rely on the recognition of oxidation and reduction, understanding the half-reactions, and possessing the ability to balance oxidation-reduction reactions. Because of these factors, the half-reaction method will be stressed in this book. 

This method of balancing oxidation-reduction reactions is somewhat similar to the half-reaction method. 

Balance the following oxidation-reduction reaction that occurs in basic solution ... 

The two balanced half-reactions need to be multiplied by factors to make certain the electrons cancel, then they can be added to produce the summation reaction for the oxidation-reduction reaction. 

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