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Chapter 1 Matter, Measurements, & Calculations

1.2 Properties and Changes

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

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Physical and Chemical Properties

In chemistry, the word physical is used to refer to processes that do not change chemical identities. Properties that can be observed without changing the identity of a substance are classified as physical properties.

Iron vs. Sulfur

Sulfur is yellow and iron is magnetic each have different properties of matter, but we can make the following observations: sulfur has color, pick up iron with a magnet, or measure its boiling point without changing its mass.

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Mass is a measure of the quantity of matter in an object.

Density is mass per unit volume. The units are grams for mass (weight) and cubic centimeter (cm3) for volume of solids or milliliters (ml) for volume of liquids

Ex. Density of lead is 11.3 g/cm3 and aluminum is 2.7 g/cm3

The mass of lead is heavier 11.3 g than aluminum that weighs 2.7 g but both solids can be compared to pieces of equal size, equal volume 1 cm3.

Don’t get mass and density confused!

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Processes that do result in chemical reactions and changes in the identity of one or more reactant are referred as chemical properties.

For ex. Gasoline burning is converted to a mixture of CO2, CO, and H2O or the combination of H2 and O2 to form H2O are classified as a chemical property.

The word chemical is used to describe processes that result in a change in identity.

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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).