Chemical equations balancing by inspection

For each reaction below, write a balanced chemical equation by inspection. 

Balancing chemical equations by inspection is a trial-and-error approach. It requires a great deal of practice, but it is very important Remember that we use the smallest whole-number coefficients. Some chemical equations are difficult to balance by inspection or trial and error. In Chapter 11 we will learn methods for balancing complex equations. 

In contrast, student performance on balancing chemical equations by inspection has been correlated with a battery of tests, including cognitive... 

Toth, Z. Balancing chemical equations by inspection. J. Chem. Educ. 74(11), 1363-1364 (1997)... 

Zoltan Toth, "Balancing Chemical Equations by Inspection," y. Chem. Educ, Vol. 74, 1997, 1363-1364. 

In Chapter 7, we learned how to balance chemical equations by inspection. Some redox reactions can be balanced in this way. However, redox reactions occurring in aqueous solutions are usually difficult to balance by inspection and require a special procedure called the half-reaction method of balancing. In this procedure, the overall equation is broken down into two half-reactions one for oxidation and one for reduction. The half-reactions are balanced individually and then added together. For example, consider tiie redox reaction ... 

If you know the reactants and products of a chemical reaction, you should be able to write an equation for the reaction and balance it. In writing the equation, first write down the correct formulas for all reactants and products. After they are written down, only then start to balance the equation. Do not balance the equation by changing the formulas of the substances involved. For simple equations, you should balance the equation by inspection. (Balancing oxidation-reduction equations will be presented in Chap. 13.) The following rules will help you to balance simple equations. 

In this chapter, you learned how to balance simple chemical equations by inspection. Then you examined the mass/mole/particle relationships. A mole has 6.022 x 1023 particles (Avogadro s number) and the mass of a substance expressed in grams. We can interpret the coefficients in the balanced chemical equation as a mole relationship as well as a particle one. Using these relationships, we can determine how much reactant is needed and how much product can be formed—the stoichiometry of the reaction. The limiting reactant is the one that is consumed completely it determines the amount of product formed. The percent yield gives an indication of the efficiency of the reaction. Mass data allows us to determine the percentage of each element in a compound and the empirical and molecular formulas. 

For each of the following unbalanced oxidation-reduction chemical equations, balance the equation by inspection, and identify which species is undergoing oxidation and which... 

The stoichiometric coefficients in a balanced chemical equation must be chosen so that the atoms of each element are conserved. Many chemical equations can be balanced by inspection. Balancing by inspection means changing stoichiometric coefficients until the number of atoms of each element is the same on each side of the arrow. Usually, we can tell what changes need to be made by looking closely at the reaction and matching the numbers of atoms of each element on both sides of the equation. Consider the following example. 

We have seen how analytical calculations in titrimetric analysis involve stoichiometry (Sections 4.5 and 4.6). We know that a balanced chemical equation is needed for basic stoichiometry. With redox reactions, balancing equations by inspection can be quite challenging, if not impossible. Thus, several special schemes have been derived for balancing redox equations. The ion-electron method for balancing redox equations takes into account the electrons that are transferred, since these must also be balanced. That is, the electrons given up must be equal to the electrons taken on. A review of the ion-electron method of balancing equations will therefore present a simple means of balancing redox equations. 

This method of balancing equations by inspection works in many, but not all, cases. Section 11.4 presents techniques for balancing certain more complex chemical equations. 

The following sample study sheet shows a procedure that you can use to balance chemical equations. It is an approach that chemists often call balancing equations by inspection. Examples 4.1 through 4.5, which follow the study sheet, will help to clarify the process. 

Kolb, D. (1981). Balancing complex redox equations by inspection. Journal of Chemical Education, 58, 642-645. 

It is extremely important to note that the reaction orders a, / , k,... are not the same as the stoichiometric coefficients a, b, c. Reaction order cannot be simply determined from inspection of the balanced chemical equation. It requires detailed information about the kinetic mechanisms underlying the reaction and can generally only be determined experimentally or through careful kinetic studies (see the dialog box on reaction mechanism for details). The overall order of the reaction is given by the sum of the reaction orders with respect to the various reactants. In other words. 

Five tasks must be performed in this problem (1) Represent the reaction by a chemical equation in which the names of reactants and products are replaced with formulas. (2) Balance the formula equation by inspection. (3) Determine the limiting reactant. (4) Calculate the theoretical yield of sodium nitrite based on the quantity of limiting reactant. (5) Use... 

This is an acid-base reaction. The other products of the reaction are Na2S04 and H2O. The reaction does not involve changes in oxidation states, and thus the equation can be balanced by inspection. The balanced chemical equation is given below ... 

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. 

A complex reacting system is defined as one that requires more than one chemical equation to express the stoichiometric constraints contained in element balances. In such a case, the number of species usually exceeds the number of elements by more than 1. Although in some cases a proper set of chemical equations can be written by inspection, it is useful to have a universal, systematic method of generating a set for a system of any complexity, including a simple system. Such a method also ensures the correct number of equations (R), determines the number (C) and a permissible set of components, and, for convenience for a very large number of species (to avoid the tedium of hand manipulation), can be programmed for use by a computer. 

Most equations are balanced by inspection. This means basically a trial-and-error, methodical approach to adjusting the coefficients. One procedure that works well is to balance the homonuclear (same nucleus) molecule last. Chemical species that fall into this category include the diatomic elements, which you should know H2, 02, N2, F2, Cl2, Br2, and I2. This is especially useful when balancing combustion reactions. If a problem states that oxygen gas was used, then knowing that oxygen exists as the diatomic element is absolutely necessary in balancing the equation correctly. 

You could balance the chemical equation for the reaction of magnesium with aluminum nitrate by inspection, instead of writing half-reactions. However, many redox equations are difficult to balance by the inspection method. In general, you can balance the net ionic equation for a redox reaction by a process known as the half-reaction method. The preceding example of the reaction of magnesium with aluminum nitrate illustrates this method. Specific steps for following the half-reaction method are given below. 

More complex chemical equations than the ones you have already tried can be balanced by using a combination of inspection and trial and error. Here, however, are some steps to follow. 

Most chemical equations can be balanced by inspection—that is, by trial and error. It is always best to start with the most complicated molecules (those containing the greatest number of atoms). For example, consider the reaction of ethanol with oxygen, given by the unbalanced equation... 

The empirical formula for a substance is the simplest ratio of the number of atoms or moles of each element. The molecular formula gives the exact number of each atom or moles of atoms in a molecule, whereas the formula unit is the empirical formula for a solid for which no discrete molecules exist. Chemical equations are balanced by inspection, ensuring that the same number of atoms of each element appears on both sides of the equation. 

Most chemical equations can be balanced by trial and error—that is, by inspection. Keep trying until you find the numbers of reactants and products that give the same number of each type of atom on both sides of the arrow. 

The balance of chemical equations occurs often by inspection, whatever this is. The... 

An inspection of the steps of the above derivation reveals what changes will be introduced by a modification in the form of the chemical equation. If the reaction were of a tjrpe where two atoms of the first species and one of the second entered the molecule, we should have for the balance-sheet of the total numbers of atoms... 

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