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Chapter 7 Chemical Reactions

7.1 Chemical Reactions

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Physical Change

In a physical change,• The identity and

composition of the substance do not change.

• The state can change or the material can be torn into smaller pieces.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Chemical Change

In a chemical change, • Reacting

substances form new substances with different compositions and properties.

• A chemical reaction takes place.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Some Examples of Chemical and Physical Changes

Table 7.1

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Classify each of the following as a

1) physical change or 2) chemical change

A. ____Burning a candle.

B. ____Ice melting on the street.

C. ____Toasting a marshmallow.

D. ____Cutting a pizza.

E. ____Polishing a silver bowl.

Learning Check

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Classify each of the following as a

1) physical change or 2) chemical change

A. 2 Burning a candle.

B. 1 Ice melting on the street.

C. 2 Toasting a marshmallow.

D. 1 Cutting a pizza.

E. 2 Polishing a silver bowl.

Solution

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Chemical Reaction

In a chemical reaction

• A chemical change produces one or more new substances.

• There is a change in the composition of one or more substances.

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Chemical Reaction

In a chemical reaction,

• Old bonds are broken and new bonds are formed.

• Atoms in the reactants are rearranged to form one or more different substances.

• Fe and O2 form rust (Fe2O3).

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Evidence of a Chemical Reaction

• Physical changes that can be seen are evidence of a chemical reaction.

Table 7.2

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Learning Check

Identify the visible evidence of a chemical reaction in each of the following:

1. Methane gas in an outdoor heater burns with a blue flame.

2. Bleach removes stains from a shirt.

3. Bubbles of CO2 are released when baking soda is mixed with vinegar.

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Solution

Identify the visible evidence of a chemical reaction in each of the following:

1. Methane gas in an outdoor heater burns with a blue flame. Heat and a flame

2. Bleach removes stains from a shirt. Color change (color removed)

3. Bubbles of CO2 are released when baking soda is mixed with vinegar. Formation of a gas (bubbles)