Name



2.4 Chemical Reactions

Chemical reactions involve chemical changes and the

conservation of mass.

Lesson Summary

Chemical Changes During a chemical change, the composition of matter changes.

A chemical change must occur for a chemical property to be observed.

The substances at the beginning of a reaction are called reactants. The substances

produced by the reaction are called products.

Reactants and products differ in composition.

Recognizing Chemical Changes Although a change in composition is the only way to

confirm a chemical change, several clues might indicate that a chemical change occurred.

One clue is a transfer of energy.

Other clues include a change in color and the production of a gas.

The formation of a precipitate, a solid that forms and settles out of a liquid, is another clue.

Conservation of Mass The law of conservation of mass says that mass is neither created

nor destroyed during a normal chemical reaction or physical change.

During chemical reactions, the total mass of the reactants equals the total mass of the

products.

Mass is also conserved during physical changes, such as a change of state.

After watching Chapter 2.4 video, answer the following questions.

Chemical Changes

1. What is a chemical property?

2. Is the following sentence true or false? Chemical properties are observed only when

a substance undergoes a chemical change.

3. What happens during a chemical reaction?

4. In chemical reactions, the substances present at the start of the reaction are called

, and the substances produced are called .

5. Circle the letter of the term that best completes the sentence. A change in the

composition of matter occurs during a chemical reaction.

a. sometimes

b. rarely

c. always

d. never

6. Which representation of a chemical reaction is correct?

a. products → reactants

b. reactants → products

Recognizing Chemical Changes

7. List four possible clues to a chemical change.

8. Is the following statement true or false? If you observe a clue for chemical change, you

can be certain that a chemical change has taken place.

9. Define a precipitate.

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Conservation of Mass

10. During a chemical reaction, the mass of the products is always equal to the mass of the

.

11. The law of conservation of mass states that in any physical change or chemical reaction,

mass is neither nor .

12. Look at Figure 2.16. How do you know that mass was conserved?

END OF STUDY QUESTIONS 2.4

A camper burned a piece of paper to start a campfire. Answer these questions about burning

the paper.

a. Is burning paper a physical change or a chemical change? How do you know?

b. If you said the change was chemical, what are the reactants? What are the products?

c. The ash produced by the burning paper has much less mass than the mass of the original

paper. Was mass conserved during this change? Explain your answer.

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Name Class Date

For Questions 1–12, complete each statement by writing the correct word or words. If you

need help, you can go online.

2.1 Properties of Matter

1. For a specific substance, every sample has the same properties.

2. Solid, , and gas are all states of matter.

3. A change of state is an example of a(n) physical change.

2.2 Mixtures

4. Depending on the distribution of components, mixtures are either heterogeneous or

.

5. Mixtures can be separated by differences in the of

their components.

2.3 Elements and Compounds

6. can be broken down into simpler substances by chemical means.

7. If the composition of a material is not fixed, the material is a(n) .

8. represent compounds, and

represent elements.

9. The can be used to easily compare properties of

different elements.

2.4 Chemical Reactions

10. When a change occurs, the composition of matter changes.

11. A chemical change might have occurred if energy transfers, color changes, a gas forms,

or a(n) forms.

12. In a chemical reaction, the mass of the reactants the mass of the

products.

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Name Class Date

Review Vocabulary

Complete this puzzle using the vocabulary terms and the clues below.

Clues

1. any part of a sample with uniform composition and properties

2. the simplest type of substance

3. matter that has a uniform and definite composition

4. the type of change that results in a change in identity

5. the results of a chemical reaction

6. a row across the periodic table

7. a column down the periodic table

8. a solid formed by a chemical reaction between two liquids

9. a substance that can be broken down into simpler substances

by chemical means

10. the substances present before a chemical reaction occurs

11. the amount of space something takes up

12. another name for a homogeneous mixture

13. the state of matter that has no definite shape or volume

Terms

volume

substance

gas

solution

phase

element

compound

chemical

period

group

products

precipitate

reactants

Write and define the term found in the outlined boxes.

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Essential Understanding

2 Self-Check Activity

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