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Chapter 5 Chemical Reactions and Quantities

5.1 Chemical Changes

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Learning Goals

Identify a change in a substance as a chemical or a physical change.

Write a balanced chemical equation from the formulas of the reactants and products for a reaction.

Identify a reaction as a combination, decomposition, replacement, or combustion reaction.

Define the terms oxidation and reduction. Use Avogadro’s number to determine the number of particles in a

given number of moles. Determine the molar mass of a substance and use molar mass to

convert between grams and moles. Given a quantity in moles of reactant or product, calculate the

moles of another substance in the reaction. Given the mass in grams of a substance in a reaction, calculate

the mass in grams of another substance in the reaction. Describe exothermic reactions and factors that affect the rate of a

reaction.

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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 © 2005 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 © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Some Examples of Chemical and Physical Changes

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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 a1) 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.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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).