World of Chemistry

Steven S.Zumdahl, Susan L.Zumdahl, Donald J.DeCoste

Chapter 7

Chemical Reactions: An Introduction - all with Video Answers

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Chapter Questions

Problem 1

Review how we defined chemical change in Chapter $3 .$ Explain how the visual clues mentioned in this chapter are indicators of chemical change as defined in Chapter 3 .

Cara Oneal

Cara Oneal

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Problem 2

If a piece of blackboard chalk is heated strongly, the mass of the chalk decreases substantially, and the chalk is converted into a fine powder. What evidence is there for a chemical reaction having taken place when the chalk is heated?

Annelies Ondersma

Annelies Ondersma

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Problem 3

If you have had a clogged sink drain at your home, your parents may have have tried using a commercial drain cleaner to dissolve the clog. What evidence is there that such drain cleaners work by chemical reaction?

Cara Oneal

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Problem 4

If a bottle of aspirin is left open to the air, eventually one of the products is acetic acid (vinegar is a mixture of acetic acid and water). Is there evidence that this change represents a chemical reaction?

David Collins

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Problem 5

The substances present before a chemical reaction takes place are called the _____, and the substances present after the reaction takes place are called the _____.

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Problem 6

In an ordinary chemical reaction, _____ are neither created nor destroyed.

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Problem 7

The notation “(g)” after a substance’s formula indicates it exists in the _____ state.

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Problem 8

In a chemical equation for a reaction, the notation “(aq)” after a substance’s formula means that the substance is dissolved in _____.

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Problem 9

If calcium carbonate is heated strongly, carbon dioxide gas is driven off, leaving a residue of calcium oxide. Write the unbalanced chemical equation for this process.

Ronald Prasad

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Problem 10

Liquefied propane gas is often used for cooking in rural areas away from natural gas lines. Propane $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)$ burns in oxygen gas, producing carbon dioxide gas, water vapor, and heat. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 11

If a sample of pure hydrogen gas is ignited very carefully, the hydrogen burns gently, combining with the oxygen gas of the air to form water vapor. Write the unbalanced chemical equation for this reaction.

Cara Oneal

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Problem 12

Solid ammonium carbonate, $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3},$ is used as the active ingredient in "smelling salts." When solid ammonium carbonate is heated, it decomposes into ammonia gas, carbon dioxide gas, and water vapor. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 13

Silver oxide may be decomposed by strong heating into silver metal and oxygen gas. Write the unbalanced chemical equation for this process.

HM

Heidi Montgomery

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Problem 14

Methanol $\left(\mathrm{CH}_{3} \mathrm{OH},$ wood alcohol is an important industrial chemical. Methanol may be synthesized from carbon monoxide gas and hydrogen gas under certain conditions of
temperature and pressure. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 15

Elemental boron is produced in one industrial process by heating diboron trioxide with magnesium metal, also producing magnesium oxide. Write the unbalanced chemical equation for this process.

Stephanie L

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Problem 16

Calcium metal is moderately reactive. If pieces of calcium are added to water, the metal begins to bubble as hydrogen gas is formed. The water begins to turn cloudy as solid calcium hydroxide begins to form. Write the unbalanced chemical equation for the reaction of calcium metal with water.

Cara Oneal

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Problem 17

Phosphorus trichloride is used in the manufacture of certain pesticide and may be synthesized directly from its elements. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 18

Magnesium hydroxide has been used for many years as an antacid (“milk of magnesia”) because it reacts with the hydrochloric acid in the stomach, producing magnesium chloride and water. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 19

Nitrous oxide gas (systematic name: dinitrogen monoxide) is used by some dentists as an anesthetic. Nitrous oxide (and water vapor) can be produced in small amounts in the laboratory by careful heating of ammonium nitrate. Write the unbalanced chemical equation for this reaction.

Cara Oneal

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Problem 20

Hydrogen sulfide gas is responsible for the odor of rotten eggs. Hydrogen sulfide burns in air, producing sulfur dioxide gas and water vapor. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 21

Acetylene gas $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ is often used by plumbers, welders, and glass blowers because it burns in oxygen with an intensely hot flame. The products of the combustion of acetylene are carbon dioxide and water vapor. Write the unbalanced chemical equation for this process.

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Problem 22

If ferric oxide is heated strongly in a stream of carbon monoxide gas, it produces elemental iron and carbon dioxide gas. Write the unbalanced chemical equation for this process.

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Problem 23

The Group 2 metals $(\mathrm{Ba}, \mathrm{Ca}, \text { Sr })$ can be produced in the elemental state by the reaction of their oxides with aluminum metal at high temperatures, also producing solid aluminum oxide. Write the unbalanced chemical equations for the reactions of barium oxide, calcium oxide, and strontium oxide with aluminum.

Cara Oneal

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Problem 24

Ozone gas is a form of elemental oxygen containing molecules with three oxygen atoms, $\mathrm{O}_{3}$ . Ozone is produced from atmospheric oxygen gas, $\mathrm{O}_{2},$ by the high-energy outbursts found in lightning storms. Write the unbalanced equation for the formation of ozone gas from oxygen gas.

Cara Oneal

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Problem 25

Carbon tetrachloride may be prepared by the reaction of natural gas (methane, $\mathrm{CH}_{4}$ ) and
chlorine gas in the presence of ultraviolet light. Write the unbalanced chemical equation for this process. (HCl is also a product.)

Cara Oneal

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Problem 26

Ammonium nitrate is used as a "high-nitrogen" fertilizer, despite the fact that it is quite explosive if not handled carefully. Ammonium nitrate can be synthesized by the reaction of ammonia gas and nitric acid. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 27

The principal natural ore of lead is galena, which is primarily lead(II) sulfide. Lead(II) sulfide can be converted to lead(II) oxide and sulfur dioxide gas by heating strongly in air. Write the unbalanced chemical equation for the reaction of lead(II) sulfide with oxygen gas.

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Problem 28

At high temperatures, xenon gas will combine directly with fluorine gas to produce solid xenon tetrafluoride. Write the unbalanced chemical equation for this process.

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Problem 29

Ammonium nitrate is highly explosive if not handled carefully, breaking down into nitrogen gas, oxygen gas, and water vapor. The expansion of the three gases produced yields the explosive force in this case. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 30

Silver nitrate is used in "styptic pencils," which help to cauterize small nicks and cuts that occur during shaving. Silver nitrate can be prepared by dissolving metallic silver in concentrated nitric acid, with hydrogen gas being an additional product of the reaction. Write the unbalanced chemical equation for this process.

Cara Oneal

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Problem 31

When balancing a chemical equation, one must never change the _____ of any reactant or product.

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Problem 32

After balancing a chemical equation, we ordinarily make sure that the coefficients are the smallest _____ possible.

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Problem 33

Balance each of the following chemical equations.
$$
\begin{array}{l}{\text { a. } \mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(g)} \\ {\text { b. } \mathrm{Ag}(s)+\mathrm{H}_{2} \mathrm{S}(g) \rightarrow \mathrm{Ag}_{2} \mathrm{S}(s)+\mathrm{H}_{2}(g)} \\ {\text { c. } \mathrm{FeO}(s)+\mathrm{C}(s) \rightarrow \mathrm{Fe}(l)+\mathrm{CO}_{2}(g)} \\ {\text { d. } \mathrm{Cl}_{2}(g)+\mathrm{KI}(a q) \rightarrow \mathrm{KCl}(a q)+\mathrm{I}_{2}(s)}\end{array}
$$

Cara Oneal

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Problem 34

Balance each of the following chemical equations.
$$
\begin{array}{l}{\text { a. } \operatorname{CaF}_{2}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(l) \rightarrow \operatorname{CasO}_{4}(s)+\mathrm{HF}(g)} \\ {\text { b. } \mathrm{KBr}(s)+\mathrm{H}_{3} \mathrm{PO}_{4}(a q) \rightarrow \mathrm{K}_{3} \mathrm{PO}_{4}(a q)+\mathrm{HBr}(g)}\end{array}
$$
$$
\begin{array}{l}{\text { c. } \operatorname{TiCl}_{4}(l)+\mathrm{Na}(s) \rightarrow \mathrm{NaCl}(s)+\mathrm{Ti}(s)} \\ {\text { d. } \mathrm{K}_{2} \mathrm{CO}_{3}(s) \rightarrow \mathrm{K}_{2} \mathrm{O}(s)+\mathrm{CO}_{2}(g)}\end{array}
$$

Cara Oneal

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Problem 35

Balance each of the following chemical equations.
$$
\begin{array}{l}{\text { a. } \mathrm{SiII}_{4}(s)+\mathrm{Mg}(s) \rightarrow \mathrm{Si}(s)+\mathrm{MgI}_{2}(s)} \\ {\text { b. } \mathrm{MnO}_{2}(s)+\mathrm{Mg}(s) \rightarrow \mathrm{Mn}(s)+\mathrm{MgO}(s)} \\ {\text { c. } \mathrm{Ba}(s)+\mathrm{S}_{8}(s) \rightarrow \mathrm{BaS}(s)} \\ {\text { d. } \mathrm{NH}_{3}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{NH}_{4} \mathrm{Cl}(s)+\mathrm{NCl}_{3}(g)}\end{array}
$$

Cara Oneal

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Problem 36

Balance each of the following chemical equations.
$$
\begin{array}{l}{\text { a. } \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Na}_{2} \mathrm{CrO}_{4}(a q) \rightarrow} \\ {\mathrm{BaCrO}_{4}(s)+\mathrm{NaNO}_{3}(a q)} \\ {\text { b. } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { c. } \mathrm{CaC}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{C}_{2} \mathrm{H}_{2}(g)}\end{array}
$$

Cara Oneal

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Problem 37

Many ships are built with aluminum superstructures to save weight. Aluminum, however, burns in oxygen if there is a sufficiently hot ignition source, which has led to several tragedies at sea. Write the unbalanced chemical equation for the reaction of aluminum with oxygen, producing aluminum oxide as the product.

Cara Oneal

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Problem 38

Crude gunpowders often contain a mixture of potassium nitrate and charcoal (carbon). When such a mixture is heated until reaction occurs, a solid residue of potassium carbonate is produced. The explosive force of the gunpowder comes from the fact that two gases are also produced (carbon monoxide and nitrogen), which increase in volume with great force and speed. Write the unbalanced chemical equation for the process.

Cara Oneal

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Problem 39

The sugar sucrose, which is present in many fruits and vegetables, reacts in the presence of certain yeast enzymes to produce ethyl alcohol (ethanol) and carbon dioxide gas. Balance the following equation for this reaction of sucrose.
$$
\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q)+\mathrm{CO}_{2}(g)
$$

Cara Oneal

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Problem 40

Methanol (methyl alcohol), CH, OH, is a very important industrial chemical. Today, methanol is synthesized from carbon monoxide and elemental hydrogen. Write the balanced chemical equation for this process.

Cara Oneal

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Problem 41

The Hall process is an important method by which pure aluminum is prepared from its oxide (alumina, Al O $_{3}$ by indirect reaction with graphite (carbon). Balance the following equation, which is a simplified representation of this process.
$$
\mathrm{Al}_{2} \mathrm{O}_{3}(s)+\mathrm{C}(s) \rightarrow \mathrm{Al}(s)+\mathrm{CO}_{2}(g)
$$

Cara Oneal

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Problem 42

Iron oxide ores, commonly a mixture of FeO and $\mathrm{Fe}_{2} \mathrm{O}_{3},$ are given the general formula $\mathrm{Fe}_{3} \mathrm{O}_{4}$ . They yield elemental iron when heated to a very
high temperature with either carbon monoxide or elemental hydrogen. Balance the following equations for these processes.
$$
\begin{array}{l}{\mathrm{Fe}_{3} \mathrm{O}_{4}(s)+\mathrm{H}_{2}(g) \rightarrow \mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\mathrm{Fe}_{3} \mathrm{O}_{4}(s)+\mathrm{CO}(g) \rightarrow \mathrm{Fe}(s)+\mathrm{CO}_{2}(g)}\end{array}
$$

Cara Oneal

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Problem 43

The elements of Group 1 all react with sulfur to form the metal sulfides. Write balanced chemical equations for the reactions of the Group 1 elements with sulfur.

Cara Oneal

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Problem 44

A common experiment in chemistry classes involves heating a weighed mixture of potassium chlorate, $\mathrm{KClO}_{3},$ and potassium chloride. Potassium chlorate decomposes when heated, producing potassium chloride and oxygen gas. By measuring the volume of oxygen gas produced in this experiment, students can calculate the relative percentage of $\mathrm{KClO}_{3}$ and $\mathrm{KCl}$ in the original mixture. Write the balanced chemical equation for this process.

Cara Oneal

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Problem 45

A common demonstration in chemistry classes involves adding a tiny speck of manganese(IV) oxide to a concentrated hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2},$ solution. Hydrogen peroxide decomposes quite spectacularly under these conditions to produce oxygen gas and steam (water vapor). Manganese(IV) oxide speeds up the decomposition of hydrogen peroxide but is not consumed
in the reaction. Write the balanced equation for the decomposition reaction of hydrogen peroxide.

Cara Oneal

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Problem 46

Glass is a mixture of several compounds, but a major constituent of most glass is calcium silicate, $\mathrm{CaSiO}_{3}$ . Glass can be etched by treatment with hydrogen fluoride: HF attacks the calcium silicate of the glass, producing gaseous and water-soluble products that can be removed by washing the glass. For example, the volumetric glassware in chemistry laboratories is often graduated by using this process. Balance the following equation for the reaction of hydrogen fluoride with calcium silicate.
$$
\mathrm{CaSiO}_{3}(s)+\mathrm{HF}(g) \rightarrow \mathrm{CaF}_{2}(a q)+\operatorname{SiF}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(l)
$$

Cara Oneal

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Problem 47

If you had a "sour stomach," you might try an antacid tablet to relieve the problem. Can you think of evidence that the action of such an antacid is a chemical reaction?

Cara Oneal

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Problem 48

If solutions of potassium chromate and barium chloride are mixed, a bright yellow solid (barium chromate) forms and settles out of the mixture, leaving potassium chloride in solution. Write a balanced chemical equation for this process.

Cara Oneal

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Problem 49

When a strip of magnesium metal is heated in oxygen, it bursts into an intensely white flame and produces a finely powdered dust of magnesium oxide. Write the unbalanced chemical equation for this process.

Cara Oneal

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