Oxidation-reduction reactions balancing equations

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

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. 

A half-recution is a chemical equation representing only the oxidation or only the reduction of an oxidation-reduction reaction. Redox equations, which must be balanced for both mass and charge, can be balanced using the haff-reaction method. 

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. 

Silver chloride is the oxidized form, so we write it on top of the bracketed fraction, and silver metal is the reduced form, so we write it beneath. But we must also write a term for the chloride ion, because Cl- (aq) appears in the balanced reduction reaction in Equation (7.42). 

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. 

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... 

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) ... 

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. 

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. 

Oxidation-reduction reactions Oxidation number Oxidizing and reducing agents Ionic notation for equations Balancing oxidation-reduction equations... 

Most aqueous reaction equations can be balanced by trial and error. Oxidation-reduction reactions require a more systematic approach to balancing equations using either an acidic or basic solution. 

Our first major task of this chapter is to learn to balance equations for chemical reactions. Balancing simple equations will be covered in this chapter equations for more complicated oxidation-reduction reactions will be considered in Chapter 16. 

In Chapter 5, we learned to write formulas for ionic compounds from the charges on the ions and to recognize the ions from the formulas of the compounds. For example, we know that aluminum chloride is AICI3 and that VCI2 contains ions. We cannot make comparable deductions for covalent compounds because they have no ions there are no charges to balance. To make similar predictions for species with covalent bonds, we need to use the concept of oxidation number, also called oxidation state. A system with some arbitrary rules allows us to predict formulas for covalent compounds from the positions of the elements in the periodic table and also to balance equations for complicated oxidation-reduction reactions. 

We have already balanced a number of simple oxidation-reduction equations, starting in Chapter 8. Most combination and decomposition reactions and all single substitution and combustion reactions are oxidation-reduction reactions. However, many oxidation-reduction reactions are much more complicated than the ones we have already considered, and we must use a systematic method for balancing equations for them. Unfortunately, many different systematic methods are used, and each chemistry instructor seems to have his or her own favorite method. Most instructors will accept any valid method that a student understands, however. The method outlined here is a standard method that should be acceptable. 

Oxidation-reduction reactions are often complicated, which means that it can be difficult to balance their equations by simple inspection. Two methods for balancing redox reactions will be considered here (1) the oxidation states method and (2) the half-reaction method. 

Oxidation-reduction reactions can occur in basic as well as in acidic solutions. The half-reaction method for balancing equations is slightly different in such cases. 

Elemental boron is produced by the reduction of boron oxide by magnesium to give boron and magnesium oxide. Write a balanced equation for this reaction. 

The assignment of electrons is somewhat arbitrary, but the procedure described below is useful because it permits a simple statement to be made about the valences of the elements in a compound without considering its electronic structure in detail and because it can be made the basis of a simple method of balancing equations for oxidation-reduction reactions. 

The next step is to balance the ecjnation for the reaction. In balancing the equation for an oxidation-reduction reaction it is often vise to write the electron reactions separately (as they would occur in an electrolytic cell), and then to add them so as to cancel out the electrons. For example, ferric ion, Fe- +", oxidi/es stannous ion, Sn, to stannic ion, Sn + + + + that is, from the bipositive state to the quadripositive state. The ferric ion is itsell reduced to ferrous ion, Fe++. The two electron reactions are... 

Balance equations for oxidation-reduction reactions through the half-reaction method. 

Describe how an oxidation-reduction reaction may be broken down into two half-reactions, and explain why the latter are useful in balancing redox equations. 

You already know that chemical equations are written to represent chemical reactions hy showing what substances react and what products are formed. You also know that chemical equations must be balanced to show the correct quantities of reactants and products. Equations for oxidation-reduction reactions are no different. In this section, you ll learn a specific method to balance redox equations. 

If the reaction is an oxidation-reduction reaction, the chemical equation must be balanced in a stepwise procedure that is presented below. 

Knowing how to balance oxidation/reduction reactions is essential to understanding all the concepts covered in this chapter. Although you probably remember this technique from your general chemistry course, we present a quick review here to remind you of how the process works. For practice, complete and balance the following equation after adding H+, OH, or H2O as needed. 

Identify the oxidizing agent and the reducing agent on the left side of each equation in Problem 18-9 write a balanced equation for each half-reaction. 18-11. Consider the following oxidation/reduction reactions ... 

The balanced overall equation for the reaction now can be written as shown in Figure 16.3. This equation is the same as the equation for the formation of zinc oxide that you read at the beginning of the discussion on redox reactions. Now you know that it represents the net oxidation-reduction reaction and is the sum of an oxidation half-reaction and a reduction half-reaction. 

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