Chemical Reactions Guided Reading and Study Answer Key

Chapter 7 Answer Key

Study Guide

My Notebook

1. Answers will vary, but could include main ideas from the summary or 1 main idea from each Reading (2).
2. Students synonym answers will vary but might be similar to: review = reread; properties = characteristics; substance = matter; evidence = clue, indicate = show; occur = happen.
3. The arrow in a chemical equation separates the reactants (starting substances) from the products and shows that a chemical change is taking place.

Guided Reading

7.1 Chemical Changes

1. reactions
2. properties
3. substance
4. reactants
5. products

7.2 Conservation of Mass

6. chemical
7. mass
8. equations
9. balanced
10. coefficient

Let's Review

1. a
2. b

Check Your Understanding

Reading 7.1

1. Answers may vary. Sample answer:The formation of rust on a nail is an example of a chemical change because iron in the nail has reacted with water to form a new compound, iron oxide. The presence of a color change on the nail indicates that a chemical reaction has occurred.
2. Answer (b) is correct.
3. Answers may vary. Sample answer: In physical changes, energy is involved to change the size of a substance into smaller pieces and to change the state of matter. For example, you use energy to use a knife to cut vegetables and energy increases in a substance when it melts or goes from being a liquid to a gas. In chemical changes, energy is involved in breaking and forming chemical bonds.
4. Answers are:
1. Chemical, new substances are formed and a gas (CO2) is produced
2. Physical, the sand castle changes size and shape
3. Chemical, the egg white changes color as proteins are denatured
4. Physical, a change of size occurs
5. Chemical, the baked bread changes color as heat is used to bake it
6. Physical. Liquid water becomes water vapor
5. Evidence that a chemical reaction has occurred includes: (a) a gas is formed, (b) a new solid is produced (as a precipitate), (c) there is a temperature change, and (d) a color change occurs.
6. Reactants include: BaCO3 (solid) and HBr (in solution); products include BaBr2 (in solution), H2O (liquid), and CO2 (gas).

Reading 7.2

1. The law of conservation of mass is a principle that states that the total mass of the reactants equals the total mass of the products in a chemical reaction. This principle is used to "balance" a chemical equation for a chemical reaction so that the number of each kind of atom on the reactants side of the equation equals the number of each kind of atom on the products side. When a chemical equation is balanced, you can make predictions about how much of a certain reactant is needed to make a certain amount of a product you desire.
2. To understand the kinds of products formed in a reaction and how much is produced, you need a closed container (a closed system) so that you can capture the products. In an open system, products like gases could easily escape and be hard to quantify.
3. 10 grams - 9.3 grams = 0.7 grams, 0.7 grams of oxygen were produced in this reaction.
4. Sample answer: A subscript indicates the number of atoms of an element in a chemical formula. A coefficient indicates the amount of a molecule or compound present in a chemical equation.
5. Answers:
1. unbalanced; 2KClO3 2KCl + 3O2
2. unbalanced; 2Fe + O2 2FeO
3. balanced; 2Li + Cl2 2LiCl
4. balanced; NH3 + HCl NH4Cl
6. Answers:
1. 2BaO2(s) 2BaO (s) + O2(g)
2. Two molecules of solid barium peroxide react to produce 2 molecules of solid barium oxide and one molecule of oxygen gas.

My Notebook

Science in your mouth p.190

The change that occurs when the student places a saltine in his/her mouth is an example of a chemical change. The change of taste is an indication of this and result when a digestive enzyme (amylase) in the mouth covert the starch (amylose) in the saltine into smaller, simple sugar carbohydrates (glucose).

Solve it! p.192

Sample student answer: No, the numbers of atoms on the reactants side and the products side do not match up. On the reactants side, there are one carbon atom, four hydrogen atoms, and two oxygen atoms. On the products side, there are one carbon atom, two hydrogen atoms, and three oxygen atoms. To make the numbers match up, it looks like I need to add more oxygen to the reactants side but I'm not sure how to make the number of hydrogen atoms match up. [Students will learn in the next section how to balance chemical equations.]

Connection: Hydrogen Powered Vehicles

1. Sample answer:
   

   Hydrogren fuel cell vehicles	Internal combustion engine vehicles
   Tailpipe emissions = only water	Tailpipe emissions include carbon monoxide, carbon dioxide, nitrous oxides, sulfuric acids, and water.
   Engine powered by electricity	Engine powered by internal combustion of gasoline.
   40-60% efficient engine	20% efficient engine
   Hydrogen fuel cell vehicles can cause an increase in greenhouse gases and atmospheric pollutants (like internal combustion engine vehicles do) if the method of producing hydrogen does not rely on "clean" energy sources such as wind or solar power.

2. Hydrogen for fuel cell vehicles can be produced by electrolysis, a process in which an electrical current is used to split water molecules into hydrogen and oxygen; or gasification, a process in which natural gas is combined with steam to produce hydrogen gas.
3. Answers will vary.
4. (student reports, answers will vary)

Activity: Proving Conservation of Mass

a. - e. Since student experiments will vary, consider grading using a rubric or have students evaluate themselves using a rubric of their own design. A sample rubric can be found on p250 of this guide.

Chapter 7 Review

Vocabulary

Reading 7.1

1. chemical reaction
2. reactant
3. product
4. precipitate

Reading 7.2

5. chemical equation
6. law of conservation of mass
7. coefficient

Concepts

Reading 7.1

1. Answers are:
1. Correct
2. Incorrect. The evaporation of water is an example of a physical change.
3. Correct.
4. Incorrect. Chemical changes involve chemical reactions and energy.
5. Correct.
6. Incorrect. Frying an egg in a pan causes a chemical change in the egg.
2. Sample student answer. The human body temperature is most likely the result of chemical changes because the production of heat (and temperature changes) is one piece of evidence that chemical reactions are taking place.
3. The ice cube in the picture illustrates a physical change. Any time there is a change in state—in this case going from a solid to a liquid—a physical change is occurring.

Reading 7.2

4. Sample student answer: The results of the experiment are probably correct. However, the problem is that the experiment was probably done in an open container. When repeating the experiment, it should be done in a closed container in order to keep track of all the products formed. In this particular reaction, carbon dioxide gas is produced which probably escaped before it's mass could be determined.
5. Answers are:
1. Reactants = C6H12O6 (solid) and O2 (gas); products = CO2 (gas) and H2O (liquid)
2. The arrow means "yields" or "produces."
3. Yes the reaction is balanced. Each side has 6 carbon atoms, 12 hydrogen atoms, and 18 oxygen atoms.

Math and Writing Skills

1. Energy is used to cut the vegetables that will go on top of the pizza. This is an example of a physical change. Energy is used as bonds are broken and reformed during chemical changes while the pizza is being made. For instance, yeast creates carbon dioxide gas in the dough of the pizza. This is a chemical change.
2. The law of conservation of mass states that the mass of the matter in the container will remain the same.

Test Practice

Reading 7.1

1. Answers are:
1. Physical. In this case, the bubbles are due to the liquid water turning into water vapor. A change of state is occurring.
2. Chemical. This is a description of a double-displacement reaction in which the precipitate indicates the presence of a new compound.
3. Chemical. There is a color change from white sugar to a black substance and a new compound, water.
4. Physical. A change in size has occurred. The beaker has gone from being whole to a bunch of smaller pieces.

Reading 7.2

2. The mass of the oxygen was 3.20 grams. This was determined by subtracting 3.91 grams from 7.11 grams. According to the law of the conservation of mass, the mass of the reactants (3.20 grams + 3.91 grams) equals the mass of the products (7.11 grams).
3. The answer is (c).
4. Answers are:
1. Cl2 + 2Br 2Cl + Br2
2. Na2SO4 + BaCl2 BaSO4 + 2NaCl
3. 2ZnS + 3O2 2ZnO + 2SO2
4. Cl2 + 2KBr 2KCl + Br2
5. H2SO4 + 2NaOH Na2SO4 + 2H2O

Project - Chemistry in the human body

(Sample poster rubric)

	Does not meet expectations	Meets expectations	Exceeds expectations
Physical changes	Identifies less than 2 physical changes in food during digestion	Identifies 2 physical changes in food during digestion	Identifies more than 2 physical changes in food during digestion
Chemical changes	Identifies less than 2 chemical in food during digestion	Identifies 2 chemical in food during digestion	Identifies more than 2 chemical in food during digestion
Diagrams	Diagrams are missing one or more of the following: Show digestion from start to finish Identify areas of physical and chemical changes in food Include labels connected by lines to parts of the diagram	Diagrams Show digestion from start to finish Identify areas of physical and chemical changes in food Include labels connected by lines to parts of the diagram	Diagrams meet all listed expectations AND Include multiple views or diagrams of important body structure in digestion OR Include chemical equations describing digestion processes

Chemical Reactions Guided Reading and Study Answer Key

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