Balancing Equations

MATH SKILLS

Balancing Chemical Equations
Aluminum reacts with copper(II) chloride, CuCl2, to form copper metal and aluminum chloride, AlCl3. Write the balanced equation for this reaction. 1. Identify the reactants and products. Aluminum and copper(II) chloride are the reactants, and aluminum chloride and copper are the products. 2. Write a word equation for the reaction. aluminum + copper(II)chloride → aluminum chloride + copper 3. Write the equation using formulas for the reactants and products. Al + CuCl2 → AlCl3 + Cu 4. Balance the equation one element at a time. The same number of each type of atom must appear on both sides. So far, there are three chlorine atoms on the right and only two on the left. To balance the number of chlorine atoms, you must multiply the amount ofcopper(II) chloride by 3 and multiply the amount of aluminum chloride by 2. Al + 3CuCl2 → 2AlCl3 + Cu
Atom Al Cu Cl Reactants 1 3 6 Products 2 1 6 Balance × × √

This equation gives you two aluminum atoms on the right and only one on the left. So you need to multiply the amount of aluminum by 2. 2Al + 3CuCl2 → 2AlCl3 + Cu
Atom Al Cu Cl Reactants 2 3 6 Products 2 1 6 Balance √ × √

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Balancing Chemical Equations

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To balance the equation, multiply the amount of copper produced by 3. 2Al + 3CuCl2 → 2AlCl3 + 3Cu
Atom Al Cu Cl Reactants 2 3 6 Products 2 3 6 Balance √ √ √

Your Turn to Think
1. Combustion in automobile engines takes place when fuel and oxygen are combined and ignited in the cylinders of the engine. However, theair that provides the oxygen for combustion also introduces nitrogen into the engine. The nitrogen reacts with oxygen at the high temperatures present in the engine, producing nitrogen oxide compounds, which are a major component of smog. In one of these reactions, nitric oxide, NO, reacts with oxygen, O2, to form nitrogen dioxide, NO2. Write the balanced equation for this reaction. 2. During thecenturies following the collapse of the western Roman Empire, marble (calcium carbonate, CaCO3) was taken from the monuments of Rome and heated to form quicklime (calcium oxide, CaO), which was used to make plaster. Carbon dioxide, CO2, was also produced in this decomposition reaction. Write the balanced equation for this reaction. 3. When a match is lit, sulfur (S8) reacts with oxygen to releaseenergy and form sulfur dioxide, SO2. Write the balanced equation for this reaction. 4. Zinc reacts with water to produce zinc hydroxide, Zn(OH)2, and molecular hydrogen gas, H2. Write the balanced equation for this reaction. 5. Barium, Ba, reacts with sulfur, S8, to form barium sulfide, BaS. Write the balanced equation for this synthesis reaction. 6. Automobile airbags rely on the decomposition ofthe compound sodium azide (NaN3) to produce the nitrogen gas, N2, needed to rapidly inflate the bag. Sodium is also produced in the reaction. Write the balanced equation for this decomposition reaction. 7. A useful single-displacement reaction involves thermite, which is a mixture of aluminum and iron oxide, Fe2O3. When the thermite reaches a high temperature, the components react to producemolten iron, aluminum oxide (Al2O3), and a great deal of energy. Write the balanced equation for the thermite reaction.

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Balancing Chemical Equations continued
8. Acid indigestion can occur when the stomach produces too much hydrochloric acid, HCl. An old and effective remedy for this involves drinking a solution of baking soda (sodium hydrogencarbonate, NaHCO3), which reacts with the hydrochloric acid to produce sodium chloride (NaCl), water, and carbon dioxide. Write the balanced equation for this reaction. 9. A problem with the remedy given in problem 8 for acid indigestion is that the carbon dioxide produced can cause discomfort. In many modern antacids, the active ingredient is magnesium hydroxide, Mg(OH)2. When this compound reacts...