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Questions 1–28 and A–E
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CHAPTER 4
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Changes in matter
Checkup
1 WHAT ARE CHANGES IN MATTER? (p. 108)
1. Does each of the following phenomena describe a physical change, a chemical change or a
nuclear transformation? Explain your answers.
a) a puddle of water evaporating in the sun
A physical change, because it is a change in state.
b) propane gas burning in a barbecue
A chemical change, because it is a combustion reaction.
c) a wooden plank being sawn in half
A physical change, because it is a change in form.
d) lead turning into gold
A nuclear transformation, because atomic nuclei are rearranged.
2 CHEMICAL CHANGES (pp. 109–124)
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2. For each of the situations in the following photos, name at least one sign that a chemical
change is occurring.
A
B
A change in colour
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The release of a gas
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C
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D
The formation of a precipitate or a change in
The emission of heat or light
colour
3. Represent each of the following reactions with a chemical equation. Specify the physical state
of each substance.
a) A solid zinc atom reacts with two molecules of a solution of hydrochloric acid (HCl), to form
one molecule of zinc chloride (ZnCl2) in solution and one molecule of hydrogen gas.
Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
b) Two atoms of solid sodium react with two molecules of liquid water to form two molecules of
sodium hydroxide (NaOH) in solution and one molecule of hydrogen gas.
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
c) The reaction of one molecule of propane gas (C3H8) with five molecules of oxygen gas
produces three molecules of carbon dioxide gas and four molecules of water vapour.
d) When two molecules of sodium chloride (NaCl) in solution are mixed with one molecule of
barium nitrate (Ba(NO3)2) in solution, two molecules of sodium nitrate (NaNO3) in solution
are formed, as well as one molecule of barium chloride (BaCl2) in the form of a solid
precipitate.
2 NaCl(aq) + Ba(NO3)2(aq) → 2 NaNO3(aq) + BaCl2(s)
4. The equation for the synthesis of water is as follows: 2 H2(g) + O2(g) → 2 H2O(l). If 2 g of
hydrogen are made to react with 16 g of oxygen, what is the mass of the resulting water?
Show your calculations.
According to the law of conservation of mass, the total mass of the reactants is equal to the total mass
of the products, therefore:
16 g of oxygen + 2 g of hydrogen = 18 g of water
CHAPTER 4
Changes in matter
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C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)
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5. When magnesium is made to react with hydrochloric acid, hydrogen gas is released. If the
reaction occurs in an open beaker, what will happen to the mass of the beaker’s contents?
Explain your answer.
The mass will decrease because the hydrogen gas will escape from the beaker.
6. Is each of the following equations balanced or not? Explain your answers.
a) NA + O2 → Na2O2 No
Before the chemical reaction
Reactants
Numbers of atoms
Na + O2
1 Na atom
2 O atoms
After the chemical reaction
Product
Numbers of atoms
Na2O2
2 Na atoms
2 O atoms
b) C + O2 → CO2 Yes
Before the chemical reaction
Reactants
Numbers of atoms
C + O2
1 C atom
2 O atoms
After the chemical reaction
Product
Numbers of atoms
CO2
1 C atom
2 O atoms
c) 2 C2H2 + 5 O2 → 4 CO2 + 2 H2O Yes
Before the chemical reaction
Reactants
Numbers of atoms
2 C 2H 2 + 5 O 2
4 C atoms
4 H atoms
10 O atoms
After the chemical reaction
Products
Numbers of atoms
4 CO2 + 2 H2O
4 C atoms
4 H atoms
10 O atoms
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d) CH4 + 2 CI2 → CCI4 + 4 HCI No
Before the chemical reaction
Reactants
Numbers of atoms
CH4 + 2 Cl2
1 C atom
4 H atoms
4 Cl atoms
After the chemical reaction
Products
Numbers of atoms
CCl4 + 4 HCl
1 C atom
4 H atoms
5 Cl atoms
7. Balance each of the following equations.
a) Mg + O2 → MgO 2 Mg + O2 → 2 MgO
Mg + O2
Mg
O2
Mg
Mg
O
MgO
Mg
O
MgO
2 Mg + O2
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2 MgO
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MgO
→
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b) Fe + O2 → Fe2O3 4 Fe + 3 O2 → 2 Fe2O3
Fe + O2
Fe2O3
→
Fe
O2
Fe
O
O
Fe2O3
Fe
O2
Fe
O
O
Fe2O3
Fe
O2
Fe
O
O
Fe
Fe
4 Fe + 3 O2
2 Fe2O3
c) C3H8 + O2 → CO2 + H2O C3H8 + 5 O2 → 3 CO2 + 4 H2O
C 3H 8 + O 2
C 3H 8
CO2 + H2O
→
O2
C
H
H
O
O
CO2
H 2O
O2
C
H
H
O
O
CO2
H 2O
O2
C
H
H
O
O
CO2
H 2O
H
H
O
O
O
O
O2
O2
C 3H 8 + 5 O 2
H 2O
3 CO2 + 4 H2O
d) KOH + H2SO4 → K2SO4 + H2O 2 KOH + H2SO4 → K2SO4 + 2 H2O
KOH + H2SO4
KOH
H2SO4
KOH
K2SO4 + H2O
→
K
O
H
K
O
H
O
H
O
H
S
K2SO4 + 2 H2O
O
2 KOH + H2SO4
K2SO4 + 2 H2O
8. The equation for the formation of copper oxide (CuO) is as follows: 2 Cu + O2 → 2 CuO. If
four moles of copper are made to react with a sufficient amount of oxygen, how many moles
of copper oxide will be obtained? Show your calculations.
2 Cu
2 mol
4 mol
+
O2 → 2 CuO
2 mol
? mol
Four moles of copper oxide will be obtained.
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O
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9. Consider the following reaction: 2 Na + 2 H2O → 2 NaOH + H2. How many moles of sodium
hydroxide will be produced if 46 g of sodium are made to react completely? Show your
calculations.
2 Na
+
2 mol
45.98 g
46 g
45.98 g
46 g × 2 mol
45.98 g
2 H2O → 2 NaOH
2 mol
2 mol
36.04 g 80.00 g
? mol
2 mol
+
H2
1 mol
2.02 g
= 2.00 mol
Two moles of sodium hydroxide will be produced.
10. The equation for the synthesis of ammonia is as follows: N2 + 3 H2 → 2 NH3. Write the
equation for the decomposition of ammonia.
2 NH3 → N2 + 3 H2
11. When a solution of hydrochloric acid is mixed with sodium bicarbonate, carbon dioxide is
released according to the following equation: HCl(aq) + NaHCO3(s) → NaCl(aq) + H2O(l) + CO2(g).
Suppose that 200 mL of the hydrochloric acid solution are made to react with sufficient
sodium bicarbonate. What should the molar concentration of the solution be to obtain 4.4 g of
carbon dioxide? Show your calculations.
HCl(aq) +
NaHCO3(s) → NaCl(aq) +
H2O(l)
1 mol
1 mol
1 mol
1 mol
36.46 g
84.01 g
58.44 g
18.02 g
? mol
1 mol
1 mol × 4.4 g
= 0.1 mol (for 200 mL of solution)
44.01 g
+
CO2(g)
1 mol
44.01 g
4.4 g
44.01 g
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The concentration of the solution should be 0.5 mol/L.
12. Iron rusts in the presence of oxygen according to the following equation:
4 Fe(s) + 3 O2(g) → 2 Fe2O3(s). To obtain 20 g of rust, what mass of iron must be transformed?
Show your calculations.
4 Fe(s)
+
4 mol
223.40 g
?g
223.40 g
3 O2(g) → 2 Fe2O3(s)
3 mol
2 mol
96.00 g 319.40 g
20 g
319.40 g
223.40 g × 20 g
= 13.99 g
319.40 g
Approximately 14 g of iron must be transformed to produce 20 g of rust.
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13. Does each of the following phenomena describe an endothermic reaction or an exothermic
reaction?
a) an egg cooking
An endothermic reaction
b) the electrolysis of hydrochloric acid
An endothermic reaction
c) a battery in use
An exothermic reaction
d) 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) + energy
An exothermic reaction
e) 6 C(s) + 3 H2(g) + energy → C6H6(l)
An endothermic reaction
f) wood burning
An exothermic reaction
14. Ammonia synthesis is a reaction that is widely used in industry. Calculate the reaction energy
of the process in order to estimate the amount of energy released or absorbed.
Energy absorbed by the reactants: 946 kJ + (3 × 435 kJ) = 2251 kJ
Energy released by the products: 6 × 389 kJ = 2334 kJ
Reaction energy = 2251 kJ – 2334 kJ = –83 kJ
The reaction releases 83 kJ of energy.
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15. The synthesis of nitrogen dioxide is an endothermic phenomenon. What amount of energy
would be needed to produce six moles of NO2? Show your calculations.
N2(g) + 2 O2(g) + 67.6 kJ → 2 NO2(g)
67.6 kJ
2 mol
? kJ
6 mol
6 mol × 67.6 kJ
= 202.8 kJ
2 mol
The reaction would take 202.8 kJ of energy.
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16. The complete combustion of one mole of carbon releases 393.5 kJ of energy. To obtain
900 kJ of energy, what mass of carbon would have to be burned? Show your calculations.
C(s) + O2(g) → CO2(g) + 393.5 kJ
1 mol
393.5 kJ
12 g
393.5 kJ
?g
900 kJ
12 g × 900 kJ
393.5 kJ
= 27.4 g
Donc, il faudra 27,4 g de carbone pour produire 900 kJ.
27.4 g of carbon would be needed to produce 900 kJ of energy.
17. When solutions of hydrochloric acid (HCl) and potassium hydroxide (KOH) are mixed, the
substances react with each other.
a) What type of chemical reaction is involved?
An acid-base neutralization reaction
b) Write the chemical equation for this reaction.
HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
or H+(aq) + Cl−(aq) + K+(aq) + OH−(aq) → K+(aq) + Cl−(aq) + H2O(l)
18. In an acid-base neutralization reaction, what happens to the pH of the acid solution? Explain
your answer.
The pH increases. The pH of an acid is less than 7, and the pH of the solution resulting from a
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complete acid-base neutralization reaction is 7.
19. What is oxidation? Give two examples of oxidation.
Oxidation is a chemical change involving oxygen or a substance with properties similar to those of
oxygen.
Answers will vary. Examples: burning wood, corroding metal and the oxidation of certain fruits and
vegetables.
20. To learn how to control fires, firefighters have to study the three necessary conditions for a
fire to start. What are these conditions?
There must be an oxidizing agent and fuel, and the fuel must reach its ignition temperature.
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21. What is the difference between an oxidizing agent and a fuel? Give an example of each.
An oxidizing agent causes combustion. Answers will vary. Example: oxygen.
A fuel undergoes combustion. Answers will vary. Example: wood.
22. Does each of the following statements refer to rapid combustion, spontaneous combustion or
slow combustion?
a) A fire starts because of a gasoline-soaked rag.
Spontaneous combustion
b) Iron rusts easily in damp environments.
Slow combustion
c) A campfire draws people together with its light and warmth.
Rapid combustion
d) Many varieties of fruit rot quickly when cut and left in the open air.
Slow combustion
23. What distinguishes photosynthesis from cellular respiration? Name at least five differences.
Answers will vary. Examples:
Photosynthesis
Releases energy.
Absorbs energy.
Produces carbon dioxide.
Converts carbon dioxide.
Converts oxygen.
Produces oxygen.
Converts glucose.
Produces glucose.
Takes place in plants and animals.
Takes place only in plants.
Converts chemical energy into thermal energy
and mechanical energy.
Converts solar energy into chemical energy.
3 NUCLEAR TRANSFORMATIONS (pp. 124–131)
24. Which type of ionizing radiation, though very harmful to human health, can be blocked with a
simple sheet of paper?
Alpha particles
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Cellular respiration
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25. Food irradiation is a process that kills harmful microorganisms and prolongs the shelf life of
the food. Isotopes like cobalt-60 are used. Since ionizing radiation must travel a certain
distance and penetrate the food completely, which type of radiation would be the most
appropriate for this application? Explain your answer.
Gamma rays, because they have the greatest penetrating power of all the types of radiation.
26. Scintigraphy is a method of medical imaging used to visualize certain organs as they are
functioning. It involves a radioactive substance, which is injected into the patient. The
radioactive substances used usually have a very short half-life. Explain why they are
preferred over substances with longer half-lives.
Radioactive substances with a very short half-life are eliminated more rapidly by the body.
27. Even though radioactivity can be harmful to human health, it nonetheless provides many
advantages. Name two industrial applications of radioactivity.
– The irradiation of food to increase its shelf life
– The irradiation of certain materials to improve their quality
28. Does each of the following nuclear reactions involve fusion or fission? Explain your answers.
a)
235
92
U + 10 n →
140
54
Xe +
94
38
Sr + 2 10 n
The reaction involves fission because the products have smaller nuclei than the reactant.
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b) 21 H + 21 H → 32 He + 10 n
The reaction involves fusion because the product has a larger nucleus than the reactants.
c) 63 Be + 10 n → 42 He + 31 H
The reaction involves fission because the products have smaller nuclei than the reactant.
d) 7 N + 2 He → 8 O + 1 p+
14
4
17
1
The reaction involves fusion because the product has a larger nucleus than the reactants.
e)
27
13
1
Al + 42 He → 30
15 P + 0 n
The reaction involves fusion because the product has a larger nucleus than the reactants.
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REVIEW QUESTIONS
A. The combustion of one litre of gasoline provides approximately 30 MJ (3.0 x 107 J) of energy,
while the reaction of one mole of zinc with oxygen provides approximately 350 kJ (3.5 x 105 J).
What mass of zinc would be required to obtain as much energy as from the combustion of 20 L
of gasoline?
If 1 L of gasoline provides 30 000 000 J of energy, then
20 L of gasoline will provide 600 000 000 J of energy.
One mole of zinc weighs 65.39 g and provides 350 000 J of energy.
To obtain 600 000 000 J of energy, 112 097 g, or approximately 112 kg, of zinc are needed.
B. Gasoline is composed mostly of octane (C8H18). When octane burns in a car engine, it reacts
mainly according to the following equation:
C8H18(l) + O2(g) → CO2(g) + H2O(g) (unbalanced equation)
a) Balance this equation.
2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)
b) If a car consumes, on average, 14 kg of gasoline per week, how many moles of carbon
dioxide will it release into the air (on average) per week?
+
18 H2O
18 mol
324.36 g
The combustion of 14 kg of gasoline releases 980 moles of carbon dioxide into the air.
C. Dwindling oil reserves and climate change are spurring scientists to find alternative methods of
fuelling cars. One method is to use metal powder. For example, zinc reacts with oxygen gas to
produce solid zinc oxide (ZnO), releasing a large amount of energy in the process. Preliminary
results for this method look promising.
a) Write a balanced equation for this reaction.
2 Zn(s) + O2(g) → 2 ZnO(s)
b) What type of chemical change is involved?
Oxidation or combustion
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2 C8H18
+
25 O2 → 16 CO2
2 mol
25 mol
16 mol
228.52 g
800.00 g 704.16 g
14 000 g
? mol
228.52 g
16 mol
14 000 g × 16 mol
= 980.22 mol
228.52 g
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c) Normally, when a metal reacts with oxygen, the energy released is barely noticeable.
Explain your answer.
Normally, the reaction is one of slow combustion, so it occurs over a long period of time. The
energy released is barely noticeable because it disperses gradually into the environment.
d) Researchers believe that using metal powder to fuel cars would be less harmful to the
environment than burning gasoline. Explain your answer.
Unlike gasoline, the combustion of metal powder does not produce carbon dioxide, a greenhouse gas.
D. Is the combustion of zinc powder an endothermic or exothermic reaction? Explain your answer.
It is an exothermic reaction because it releases energy.
E. Prepare your own summary of Chapter 4 by building a concept map.
See the Concept maps section in Guide B.
Follow-up
1. Why is it difficult to protect people from the radiation given off by radioactive elements? Why is
this radiation harmful to human health?
Some radiation, such as gamma rays, is stopped only by high-density materials, like concrete or lead,
so it passes easily through the human body. Radiation can be harmful to health because of its ability to
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alter a cell’s DNA, which can lead to the development of cancer cells.
2. Cesium-137 has a half-life of about 30 years. Is it normal that after more than 20 years, levels
of radioactivity in the ground near Chernobyl are still very high? Explain your answer.
Yes, because a half-life of 30 years means that it takes 30 years for half of the amount of cesium to
decay. Therefore, after 20 years, more than half of the cesium still remains in the ground.
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