Chemical Reactions

Unit 2: Chemical Reactions
Chapter 4: The Effects of Chemical Reactions
Section 4.1: Introduction to Chemical Reactions, pages 53–54
1. A physical change in a substance occurs when a substance changes its form or state. Physical change does
not require a change in the chemical identity of the substance.
2. A chemical change in a substance occurs when the substance is changed into a different substance.
3. Table 1 Chemical and Physical Changes
The reaction
Type of change that occurred
Water is heated in a pot on the stove and becomes vaporized.
physical change
Water and metal react to form rust.
chemical change
A snowball melts in your hand.
physical change
Hydrogen peroxide is mixed with water to form hydrogen and
chemical change
oxygen gas.
4. A change in colour, the release of a gas, the release of thermal energy, and the formation of a solid residue
are all clues that a chemical reaction has taken place.
5. (a) No. A chemical change does not occur when water is boiled on a stove, producing a gas.
(b) To prove this, the product produced (the gas) must be tested to see if it is chemically different from the
starting material (the water).
6. The solid produced in the reaction liquid + liquid → solid is called a precipitate.
7. Table 2 Identification of Materials
8. The concept that in a chemical reaction the mass of the reactants equals the mass of the products is known as
the law of conservation of mass.
9. Table 3 Identification of State Symbol
State symbol Meaning
10. Table 4 Balancing Equations
word equation
water → hydrogen + oxygen
skeleton equation
H2 O(l) → H2(g) + O2(g)
balanced chemical equation
2 H2O(l) → 2 H2(g) + O2(l)
11. (a) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)
(b) 2 Mg(s) + O2(g) → 2 MgO(s)
(c) 2 Fe(s) + 3 Cl2(g) → 2 FeCl3 (aq)
(d) 2 C2 H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l)
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Chapter 4: The Effects of Chemical Reactions
Section 4.2: Synthesis and Decomposition Reactions, pages 55–57
1. b
2. Answers may vary but should include two of the following: lithium, sodium, rubidium, or cesium. Sample
answer: Based on potassium’s reactivity with chlorine, two other elements that will react with chlorine are
lithium and sodium.
3. In a synthesis reaction, two reactants collide, breaking the existing bonds between their atoms, and form new
bonds. In this process, a new compound is formed. The product is typically larger and more complex.
4. Table 1 Synthesis Reaction for Sodium and Oxygen
word equation
sodium + oxygen → sodium oxide
Na(s) + O2 (g) → Na2 O(s)
skeleton equation
4 Na(s) + O2(g) → 2 Na2O(s)
5. False. Group 1 elements, which include alkali metals, typically form ionic compounds. (Hydrogen forms
molecular compounds.)
6. Molecular compounds are made up of atoms.
7. Table 2 Completing and Balancing Equations for Synthesis Reactions
Balanced equation
N2(g) + H2(g)
N2(g) + 3 H2(g) → 2 NH3 (g)
balanced chemical equation
Li(s) + Cl2(g)
2 Li(s) + Cl2(g) → 2 LiCl(s)
Al(s) + Br2(g)
2 Al(s) + 3 Br2(g) → 2 AlBr3(s)
2 K(s) + S(s) → K2S(s)
8. Synthesis reactions with can be difficult to predict when they are a reaction between non-metals other than
hydrogen because the products of these reactions often depend on the reaction conditions.
9. d
10. True
11. In a decomposition reaction, a larger or more complex compound breaks down to form two (or more)
simpler products.
12. In a synthesis reaction, two reactants combine to make a larger or more complex product. Decomposition
reactions occur in the opposite manner. One larger or more complex reactant breaks down to form two (or
more) simpler products.
13. Table 3 A Decomposition Reaction
word equation
hydrogen chloride→ hydrogen + chloride
K(s) + S(s)
skeleton equation
HCl(g) → H2 (g) + Cl2(g)
2 HCl(g) → H2(g) + Cl2 (g)
14. Table 4 Completing and Balancing Equations for Decomposition Reactions
Balanced equation
Ni(s) + O2(g)
2 Ni2O3(s) → 4 Ni(s) + 3 O2(g)
balanced chemical equation
Al(s) + O2(g)
2 Al2O3(s) → 4 Al(s) + 3 O2(g)
Ca(s) + P(s)
Ca3P2(s) → 3 Ca(s) + 2 P(s)
Na2CO3 (s)
Na2O(s) + CO2(g)
Na2CO3(s) → Na2O(s) + CO2(g)
15. Table 5 Types of Reactions
H2CO3(aq) → H2O(l) + CO2(g)
Type of Reaction
2 Mg(s) + 2 O2(g) → 2 MgO(s)
H2SO3(aq) → H2O(l) + SO2(g)
2 P(s) + 3 Cl2(g) → 2 PCl3(g)
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Chapter 4: The Effects of Chemical Reactions
Section 4.3: Explore an Issue in Chemical Reactions: Garbage Gasification
—A Heated Debate, page 58
1. Gasification is heating waste to temperatures high enough to cause the molecules of the waste substances to
decompose into simpler substances.
2. The transformation of large compounds into the component parts of syngas represents decomposition.
3. (a) Using syngas to create methanol, CH3OH(g), is a synthesis reaction.
(b) Skeleton equation for this reaction: H2(g) + CO(g) → CH3OH(g)
(c) Balanced equation for this reaction: 2 H2(g) + CO(g) → CH3OH(g)
4. Steps involved in the critical thinking process for determining the solution for an environmental problem
include research, determination of benefits and drawbacks of possible solutions, identification of alternatives,
comparison of solutions, decision making, and communication.
5. (a).Table 1 Benefits and Drawbacks of Gasification
Benefits of gasification
Drawbacks of gasification
• safe
• produces harmful emissions that may damage human
• produces energy that can be sold
• cost-effective
• may undermine recycling progress already made
• addresses the problem of increasing quantities • unknown environmental risks
of waste
(b) The hazardous materials created by the process of gasification include acids, heavy metals, and ash.
Section 4.4: Single Displacement Reactions, pages 59–61
1. Single displacement reactions often are used when metals need to be recovered from a solution.
2. (a) Table 1 A Single Displacement Reaction
word equation
zinc + copper chloride → zinc chloride + copper
skeleton equation
Zn(s) + CuCl2(l) → ZnCl2(l) + Cu(s)
Zn(s) + CuCl2(l) → ZnCl2(l) + Cu(s)
(b) The solid copper formed in this reaction is known as a precipitate.
3. (a) Reactants (given): Mg(s) + HCl(l)
Products: MgCl(s) + H2(g)
Balanced equation: 2 Mg(s) + 2 HCl(l) → 2 MgCl(s) + H2(g)
(b) Reactants (given): Zn(s) + H2SO4(l)
Products: ZnSO4(l) + H2(g)
Balanced Equation: Zn(s) + H2SO4(l) → ZnSO4 (l) + H2 (g)
(c) Reactants (given): Cu(s) + AgNO3(aq)
Products: Ag(s) + Cu(NO3)2(aq)
Balanced Equation: Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + Cu(NO3)2(aq)
4. An activity series is a ranking of the relative reactivity of metals or halogens in single displacement
reactions. The more reactive the element, the higher it is listed in the activity series. An elements can displace
any elements below it in the activity series.
5. False. The most reactive metals are at the top of the activity series.
6. Two important generalizations about activity series are: 1) An element higher on the list is able to replace
any element below it on the list. 2) The farther apart two elements are in an activity series, the more likely it is
that the displacement reaction will occur quickly.
balanced chemical equation
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Chapter 4: The Effects of Chemical Reactions
7. (a) Potassium will replace sodium in a single displacement reaction because it is more reactive than sodium.
(b) Platinum will not replace chromium in a single displacement reaction because platinum is less reactive than
(c) Table 2 Single Displacement Reactions
Products of Reaction
no reaction
Al2O3(aq) + 2 Fe(s) →
2 Al(s) + Fe2O3(aq) →
Al2O3(aq) + 2 Fe(s)
Cl2(g) + 2 KBr(aq) →
2 KCl(aq) + Br2(l)
no reaction
Al(s) + MgCl2(aq) →
8. a
9. A different pattern is used to predict the reactivity of halogens because displacement of a halogen involves
the displacement of a negative ion (anion) rather than a positive ion (cation).
10. (a) Cl2(aq) + 2 NaBr(aq) → Br2(aq) + 2 NaCl(aq)
(b) Br2(g) + 2KI(s) → 2 KBr(s) + I2(g)
(c) Br2(g) + 2 NaCl(aq): No reaction occurs between these reactants because bromine is lower on the activity
series for the halogens than chlorine.
11. Sodium hydrogen carbonate, NaHCO3, is effective for neutralizing stomach acid, HCl, because
hydrochloric acid reacts in a displacement reaction with sodium hydrogen carbonate to form sodium chloride,
water, and carbon dioxide. The sodium replaces the hydrogen in the hydrochloric acid, forming sodium
chloride, or table salt. This reduces the quantity of stomach acid present and the painful burning sensation
caused during indigestion.
Section 4.5: Chemistry Journal: The Mystery of the Missing Mercury, page 62
1. Mercury disappears from the Arctic air during the spring when highly reactive bromine atoms, Br0, in
seawater react with oxygen in the air to produce bromine monoxide, BrO. Bromine monoxide is also highly
reactive. Scientists think both bromine and bromine monoxide react with mercury in the air, pulling away two
of its electrons to leave a mercury(II) ion, Hg2+, that can attaches itself to snowflakes and fall to the ice surface.
2. Mercury remains in the environment for a long time because it has a very low level of reactivity. Looking at
the reactivity series, it is evident that there are few elements that would be capable of replacing the element in
a displacement reaction. In most instances, mercury will come into contact with compounds that contain
elements that are more reactive.
3. Large amounts of mercury can be found in our environment because the combustion of coal releases
mercury into the atmosphere. Small quantities of mercury also enter the atmosphere from volcanic activity.
Wind can transport mercury in the atmosphere all over the globe.
4. Some of the challenges that exist for furthering research regarding the missing mercury in the Arctic are the
huge size of the Arctic, a landscape that is difficult to navigate, the extreme climate, plus the costs involved in
overcoming these challenges.
5. Mercury attached to carbon atoms poses a unique threat to human and animal health because it is more
likely to enter the bodies of organisms and to bioaccumulate. Once in the body, it can harm the nervous
system, because it is a potent neurotoxin.
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Chapter 4: The Effects of Chemical Reactions
Section 4.6: Double Displacement Reactions, pages 63–64
1. c
2. False. A substance is described as very soluble if a significant quantity of the substance dissolves.
3. Table 1 A Double Displacement Reaction for Calcium Carbonate and Hydrochloric Acid
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO3(s) + HCl(l) → CaCl2(s) + H2 O(l) + CO2 (g)
CaCO3(s) + 2 HCl(l) → CaCl2 (s) + H2 O(l) + CO2(g)
4. (a) Reactants (given): KOH(l) + H2SO4(l)
Products:K2SO4(s)+ H2O(l)
Balanced equation: 2 KOH(l) + H2SO4(l) → K2SO4(s)+ 2 H2O(l)
(b) Reactants (given): FeS(s) + HCl(l)
Products: FeCl2(s)+ H2S(g)
Balanced Equation: FeS(s) + 2 HCl(l) → FeCl2(s)+ H2S(g)
(c) Reactants (given): NaCl(s) + H2SO4(l)
Products: Na2SO4(s)+ HCl(l)
Balanced Equation: 2 NaCl(s) + H2SO4(l) → Na2SO4(s)+ 2 HCl(l)
5. In the equation NaCl(s) + H2O(l) → Na–(aq) + Cl+(aq), NaCl is the solute and H2O is the solvent.
6. Table 2 Double Displacement Reactions
Products of Reaction
no reaction
CaBr2 + 2 KOH →
Cu(OH)2 + 2 HC2H3O2 →
Cu(C2 H3O2) 2 + 2 H2 O
FeS + 2 HCl →
FeCl2 + H2S
no reaction
Ca(NO3)2 + 2 HCl →
7. Cl and NO3 are both highly soluble. NO3 will have no exceptions. However, Cl is not highly soluble when it
is attached to Ag. Thus, while it may be possible for the KNO3 to dissolve into its anion and cation parts, AgCl
will not be soluble, preventing a reaction from occurring.
8. H2CO3(aq) → H2O(l) + CO2(g)
9. A neutralization reaction creates a solution in which the pH of the final product is closer to 7 (neutral) than
the pH of either of the reactants. A reaction can be confirmed by measuring the pH of the final solution and
comparing it with the pH of the reactant solutions.
10. (a) HCl(l) + NaOH(aq) → NaCl(s)+ H2O(l)
(b) H2SO4 (l)+ 2 NH4OH(l) → (NH4)2SO4 (l)+ 2 H2O(l)
(c) 2 NaOH(aq) + H2CO3 (l) → Na2CO3(aq) + 2 H2O(l)
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Chapter 4: The Effects of Chemical Reactions
Chapter 4 Summary, page 65
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Chapter 4: The Effects of Chemical Reactions
Chapter 4 Questions, pages 66–67
1. d
2. a
3. (a) True
(b) False. In a neutralization reaction, no precipitate is formed.
4. Single displacement reactions involve the displacement of one element in a compound to produce one new
element and one new compound. Double displacement reactions involve the displacement of two elements in
two different compounds, producing two new compounds.
5. A single displacement reaction will not occur between Al(s) and MgCl2(aq) because magnesium is more
reactive than aluminum. If the more reactive element is attached in the compound, the less reactive element
cannot react.
6. A double displacement reaction will not occur between calcium bromide, CaBr2, and potassium hydroxide,
KOH, because the products of the reaction do not include water, a gas, or a precipitate. Both of the products
formed in the reaction, calcium hydroxide, Ca(OH)2, and potassium bromide, KBr, are highly soluble and will
remain in the aqueous form.
7. (a) A chemical reaction has occurred if energy is released, the solution changes colour, or a gas is released.
(b) Another observable change indicating that a chemical reaction has occurred is that a precipitate has formed.
(c) If no observable change occurred, the pH of the solution could be measured and compared to the pH of
each reactant to determine the presence of a chemical reaction.
8. Table 1 Identification of Materials
2 SO3
2 SO2
9. Table 2 Classification of Reactions
NaCO3(s) → NaO(s) + CO2(g)
Type of Reaction
Zn(s) + CuCl2(l) → ZnCl2 (l) + Cu(s)
single displacement
4 Na(s) + O2(g) → 2 Na2O(s)
CaCO3 (s) + 2 HCl(l) → CaCl2(s) + H2 O(l) + CO2(g)
double displacement
2 KOH(l) + H2SO4 (l) → K2SO4 (s)+ 2 H2O(l)
double displacement
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Chapter 4: The Effects of Chemical Reactions