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Chapter 7
Chemical Reactions

07-01
Title
Chemistry occurs in an automobile engine
Caption
A chemical reaction between octane (gasoline) and oxygen produces gaseous carbon dioxide and water. The gases move the engine's pistons, which, in turn, propel the car.
Notes
Students might explore the question of where the energy comes from to move the engine's pistons.
Keywords
octane, oxygen, carbon dioxide, water, combustion, hydrocarbon
07-05-01un
Title
A chemical equation describes the combustion of natural gas
Caption
In this reaction, the equation suggests that the two oxygen atoms in O2 produce three oxygen atoms in the products: two in CO2 and one in H2O. Such a result would violate the Law of Conservation of Mass. By balancing the equation, we can show that the Law of Conservation of Mass is indeed obeyed.
Notes
All chemical equations must obey the Law of Conservation of Mass.
Keywords
methane, oxygen, chemical equation, combustion, carbon dioxide, water
07-05-02un
Title
A chemical equation describes the combustion of natural gas
Caption
In this reaction, the equation suggests that the four hydrogen atoms in CH4 produce two hydrogen atoms in the products: two in H2O. Such a result would violate the Law of Conservation of Mass. By balancing the equation, we can show that the Law of Conservation of Mass is indeed obeyed.
Notes
All chemical equations must obey the Law of Conservation of Mass.
Keywords
methane, oxygen, chemical equation, combustion, carbon dioxide, water
07-05-04f
Title
Salt dissolving in glass of water
Caption
Salt (NaCl) separates into independent Na+ and Cl- ions when mixed with water.
Notes
The polar water molecules, with their positive and negative regions, attract both the sodium and chloride ions well enough to pull the ions apart from one another.
Keywords
ion, anion, cation, solution, ionic compound, sodium chloride, solubility
07-06-01g
Title
Silver nitrate dissolving in water
Caption
Silver nitrate (AgNO3) separates into independent Ag+ and NO3- ions when mixed with water.
Notes
The polar water molecules, with their positive and negative regions, attract both the Ag+ and NO3- ions well enough to pull the ions apart from one another.
Keywords
ion, anion, cation, solution, ionic compound, silver nitrate, solubility
07-06-02h
Title
Silver chloride does not dissolve in water
Caption
The silver ions and chloride ions attract one another so strongly that the polar water molecules cannot overcome the attraction to dissolve the AgCl. The silver chloride remains a white solid at the bottom of the water.
Notes
Precipitates such as silver chloride will dissolve in water to a limited extent; study of this phenomenon uses the concept of equilibrium.
Keywords
ion, anion, cation, solution, ionic compound, silver chloride, solubility, precipitate
07-08-03un
Title
Example of a reaction that could produce a precipitate
Caption
When two ionic compounds combine, the ions may recombine to form a precipitate. In this example, Pb2+ and I- combine to form insolublePbI2—a precipitate.
Notes
The solubility of the two original ionic compounds in water allows the ions to recombine to form a potentially insoluble product.
Keywords
precipitate, lead, iodine, lead iodide, ionic compound, solubility
07-08-04k
Title
Illustration of a reaction that produces a precipitate
Caption
When two ionic compounds combine, the ions may recombine to form a precipitate. In this example, Pb2+ and I- combine to form insoluble PbI2—a precipitate.
Notes
The solubility of the two original ionic compounds in water allows the ions to recombine to form a potentially insoluble product.
Keywords
precipitate, lead, iodine, lead iodide, ionic compound, solubility
07-08-05un
Title
Ions recombine to form a precipitate
Caption
When sodium carbonate and copper(II) chloride are mixed, the ions can recombine to form a precipitate. In this case, the two products are NaCl and CuCO3. The CuCO3 is insoluble.
Notes
This reaction can also be studied using the principle of equilibrium.
Keywords
precipitate, copper, carbonate, copper(II) carbonate, ionic compound, solubility
07-08-06un
Title
Ions may fail to form a precipitate
Caption
When lithium nitrate and sodium sulfate are mixed, the ions have an opportunity to recombine to form a precipitate. In this case, however, the two products are NaNO3 and Li2SO4. Both are soluble, so no precipitate forms.
Notes
This reaction can also be studied using the principle of equilibrium.
Keywords
precipitate, lithium, sulfate, sodium, nitrate, lithium sulfate, sodium nitrate, ionic compound, solubility
07-08-07un
Title
Will Pb(C2H3O2)2(aq) + Na2SO4(aq) form a precipitate?
Caption
When Pb(C2H3O2)2 and Na2SO4 are mixed, the ions can recombine to form a precipitate. In this case, the two products are NaC2H3O2 and PbSO4. The PbSO4 is insoluble.
Notes
This reaction can also be studied using the principle of equilibrium.
Keywords
precipitate, lead, acetate, sodium, sulfate, lead(II) sulfate, sodium acetate, ionic compound, solubility
07-08-08un
Title
Spectator ions
Caption
Ions that remain unchanged on each side of the equation's arrow are called spectator ions. These ions ensure that the charge remains balanced throughout the reactions, but they do not form precipitates.
Notes
Spectator ions are often ignored when precipitation reaction equations are written.
Keywords
precipitate, spectator ion, ionic compound, solubility
07-08-09un
Title
Spectator ions
Caption
Ions that remain unchanged on each side of the equation's arrow are called spectator ions. These ions ensure that the charge remains balanced throughout the reactions, but they do not form precipitates.
Notes
Spectator ions are often ignored when precipitation reaction equations are written.
Keywords
precipitate, spectator ion, ionic compound, solubility
07-08-16un
Title
Example of a gas evolution reaction
Caption
When nitric acid and sodium carbonate are mixed, the ions can recombine to form a soluble salt (sodium nitrate), and carbonic acid, H2CO3. The carbonic acid decomposes into water and carbon dioxide gas.
Notes
Carbonic acid will always decompose to carbon dioxide and water.
Keywords
gas evolution reaction, gas, carbon dioxide, ionic compound, nitric acid, sodium carbonate
07-08-20r
Title
Classifying simple chemical reactions by observed phenomenon
Caption
The chemical reactions studied in Chapter 7 belong to four categories: precipitation, acid–base, gas evolution, and oxidation–reduction. Combustion reactions are a variety of the oxidation–reduction type.
Notes
This classification system focuses on the type of chemistry or phenomenon observed during the reaction.
Keywords
precipitation, acid–base, gas evolution, oxidation–reduction, combustion, chemical reaction, classification
07-08-24v
Title
Classifying simple chemical reactions at the atomic level
Caption
The chemical reactions studied in Chapter 7 can be classified in four categories: synthesis, decomposition, single displacement, and double displacement.
Notes
This classification system focuses on the interactions between the atoms involved.
Keywords
synthesis, decomposition, single displacement, double displacement, chemical reaction, classification

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