Changes in matter - Westmount High School | Dux vitæ...

Name: ______________________________________ Group: ______________ Date: ___________

CHAPTER 4 Checkups and follow-ups Changes in matter

1 Observatory / Guide

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ANSWER KEY

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

b) propane gas burning in a barbecue

c) a wooden plank being sawn in half

d) lead turning into gold

2 CHEMICAL CHANGES (pp. 109–124) 2. For each of the situations in the following photos, name at least one sign that a chemical

change is occurring.

A change in colour

The release of a gas

A physical change, because it is a change in state.

A chemical change, because it is a combustion reaction.

A physical change, because it is a change in form.

A nuclear transformation, because atomic nuclei are rearranged.

A B

ANSWER KEY

Checkups and follow-ups EST Questions 1–28 and A–E

CHAPTER 4

Name: ______________________________________ Group: ______________ Date: ___________

CHAPTER 4 Changes in matter Checkups and follow-ups


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ANSWER KEY

The formation of a precipitate or a change in colour

The emission of heat or light

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.

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.

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.

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.

Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)

2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

2 NaCl(aq) + Ba(NO3)2(aq) → 2 NaNO3(aq) + BaCl2(s)

C D

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

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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.

6. Is each of the following equations balanced or not? Explain your answers. a) NA + O2 → Na2O2 No

Before the chemical reaction After the chemical reaction

Reactants Numbers of atoms Product Numbers of atoms Na + O2

1 Na atom 2 O atoms

Na2O2 2 Na atoms 2 O atoms

b) C + O2 → CO2 Yes

Before the chemical reaction After the chemical reaction Reactants Numbers of atoms Product Numbers of atoms

C + O2

1 C atom 2 O atoms

CO2 1 C atom 2 O atoms

c) 2 C2H2 + 5 O2 → 4 CO2 + 2 H2O Yes

Before the chemical reaction After the chemical reaction Reactants Numbers of atoms Products Numbers of atoms

2 C2H2 + 5 O2

4 C atoms 4 H atoms 10 O atoms

4 CO2 + 2 H2O 4 C atoms 4 H atoms 10 O atoms

d) CH4 + 2 CI2 → CCI4 + 4 HCI No

Before the chemical reaction After the chemical reaction Reactants Numbers of atoms Products Numbers of atoms

CH4 + 2 Cl2

1 C atom 4 H atoms 4 Cl 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 → MgO

Mg O2

Mg

Mg O

Mg O

MgO

MgO

2 Mg + O2 2 MgO

The mass will decrease because the hydrogen gas will escape from the beaker.

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

b) Fe + O2 → Fe2O3

4 Fe + 3 O2 → 2 Fe2O3 Fe + O2 → Fe2O3

Fe O2

Fe O2

Fe O2

Fe

Fe O O

Fe O O

Fe O O

Fe

Fe2O3

Fe2O3

4 Fe + 3 O2 2 Fe2O3

c) C3H8 + O2 → CO2 + H2O

C3H8 + 5 O2 → 3 CO2 + 4 H2O

C3H8 + O2 → CO2 + H2O

C3H8 O2

O2

O2

O2

O2

C H H O O

C H H O O

C H H O O

H H O O

O O

CO2 H2O

CO2 H2O

CO2 H2O

H2O

C3H8 + 5 O2 3 CO2 + 4 H2O

d) KOH + H2SO4 → K2SO4 + H2O

2 KOH + H2SO4 → K2SO4 + 2 H2O

KOH + H2SO4 → K2SO4 + H2O

KOH H2SO4

KOH

K O H S

K O H

O H

O H

O

O

K2SO4 + 2 H2O

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 + O2 → 2 CuO 2 mol 2 mol 4 mol ? mol

Four moles of copper oxide will be obtained.

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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 H2O → 2 NaOH + H2 2 mol 2 mol 2 mol 1 mol 45.98 g 36.04 g 80.00 g 2.02 g 46 g ? mol 45.98 g 2 mol 46 g × 2 mol

45.98 g

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) + CO2(g) 1 mol 1 mol 1 mol 1 mol 1 mol 36.46 g 84.01 g 58.44 g 18.02 g 44.01 g ? mol 4.4 g 1 mol 44.01 g 1 mol × 4.4 g 44.01 g

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) + 3 O2(g) → 2 Fe2O3(s) 4 mol 3 mol 2 mol 223.40 g 96.00 g 319.40 g ? g 20 g 223.40 g 319.40 g 223.40 g × 20 g 319.40 g

Approximately 14 g of iron must be transformed to produce 20 g of rust.

= 2.00 mol

= 0.1 mol (for 200 mL of solution)

= 13.99 g

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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.

The reaction releases 83 kJ of energy.

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.

The reaction would take 202.8 kJ of energy.

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

N2(g) + 2 O2(g) + 67.6 kJ → 2 NO2(g)

67.6 kJ 2 mol

? kJ 6 mol

6 mol × 67.6 kJ 2 mol

= 202.8 kJ

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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.

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?

b) Write the chemical equation for this reaction.

18. In an acid-base neutralization reaction, what happens to the pH of the acid solution? Explain your answer.

19. What is oxidation? Give two examples of oxidation.

20. To learn how to control fires, firefighters have to study the three necessary conditions for a fire to start. What are these conditions?

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

Donc, il faudra 27,4 g de carbone pour produire 900 kJ.

An acid-base neutralization reaction

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) or H+

(aq) + Cl−(aq) + K+(aq) + OH−(aq) → K+(aq) + Cl−(aq) + H2O(l)

The pH increases. The pH of an acid is less than 7, and the pH of the solution resulting from a complete acid-base neutralization reaction is 7.

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.

There must be an oxidizing agent and fuel, and the fuel must reach its ignition temperature.

= 27.4 g

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

21. What is the difference between an oxidizing agent and a fuel? Give an example of each.

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.

b) Iron rusts easily in damp environments.

c) A campfire draws people together with its light and warmth.

d) Many varieties of fruit rot quickly when cut and left in the open air.

23. What distinguishes photosynthesis from cellular respiration? Name at least five differences. Answers will vary. Examples:

Cellular respiration 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?

An oxidizing agent causes combustion. Answers will vary. Example: oxygen. A fuel undergoes combustion. Answers will vary. Example: wood.

Spontaneous combustion

Slow combustion

Rapid combustion

Slow combustion

Alpha particles

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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.

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.

27. Even though radioactivity can be harmful to human health, it nonetheless provides many advantages. Name two industrial applications of radioactivity.

28. Does each of the following nuclear reactions involve fusion or fission? Explain your answers.

a) U + n → Xe + Sr + 2 n

b) H + H → He + n

c) Be + n → He + H

d) N + He → O + p+

e) Al + He → P + n

Gamma rays, because they have the greatest penetrating power of all the types of radiation.

Radioactive substances with a very short half-life are eliminated more rapidly by the body.

– The irradiation of food to increase its shelf life

– The irradiation of certain materials to improve their quality

The reaction involves fission because the products have smaller nuclei than the reactant.

The reaction involves fusion because the product has a larger nucleus than the reactants.

The reaction involves fission because the products have smaller nuclei than the reactant.



235 92 1

0 140 54

94 38

1 0

1 0

2 1

2 1

3 2

6 3

1 0

4 2

3 1

14 7

4 2

17 8

1 1

27 13

4 2

30 15

1 0

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

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?

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.

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?

2 C8H18 + 25 O2 → 16 CO2 + 18 H2O 2 mol 25 mol 16 mol 18 mol 228.52 g 800.00 g 704.16 g 324.36 g 14 000 g ? mol 228.52 g 16 mol 14 000 g × 16 mol 228.52 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.

b) What type of chemical change is involved?

2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)

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.

2 Zn(s) + O2(g) → 2 ZnO(s)

Oxidation or combustion

= 980.22 mol

Name: ______________________________________ Group: ______________ Date: ___________



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ANSWER KEY

c) Normally, when a metal reacts with oxygen, the energy released is barely noticeable. Explain your answer.

d) Researchers believe that using metal powder to fuel cars would be less harmful to the environment than burning gasoline. Explain your answer.

D. Is the combustion of zinc powder an endothermic or exothermic reaction? Explain your answer.

E. Prepare your own summary of Chapter 4 by building a concept map.

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?

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.

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 alter a cell’s DNA, which can lead to the development of cancer cells.

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.

See the Concept maps section in Guide B.

Unlike gasoline, the combustion of metal powder does not produce carbon dioxide, a greenhouse gas.

It is an exothermic reaction because it releases energy.

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.

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