5 2 how matter changes (physical sciences)

California Leveled Science Readers (Grade 5) Content leveled readers teach science concepts, vocabulary, and reading skills – at each student’s reading level – and allow students to read and explore the wonders of nonfiction. Leveled science readers deliver science content to help address the individual needs of all students. They reinforce reading skills and strategies while promoting science understanding. Each grade 5 science reader is a richly illustrated, selfcontained little book with 10 to 14 double pages. BELOW 5.1 Building Blocks of Matter (Physical Sciences) 5.2 Changes in Matter (Physical Sciences) 5.3 Basic Structures of Organisms (Life Sciences) 5.4 MISSING 5.5 Water on Earth (Earth Sciences) 5.6 Weather (Earth Sciences) 5.7 The Solar System (Earth Sciences) ON 5.1 Understanding Matter (Physical Sciences) 5.2 How Matter Changes (Physical Sciences) 5.3 The Building Blocks of Organisms (Life Sciences) 5.4 Systems of the Human Body (Life Sciences) 5.5 Earths Hydrosphere (Earth Sciences) 5.6 How Weather Works (Earth Sciences) 5.7 Earths Solar System (Earth Sciences) ADVANCED 5.1 Atoms (Physical Sciences) 5.2 Acids and Bases at Work (Physical Sciences) 5.3 MISSING 5.4 MISSING 5.5 MISSING 5.6 Hurricanes (Earth Sciences) 5.7 The Red Planet (Earth Sciences)

Genre Comprehension Skill Text Features Science Content

Nonfi ction Draw Conclusions • Captions

• Charts

• Labels

• Glossary

Changes in Matter

Scott Foresman Science 5.2

Standards Preview

Standard Set 1 Physical Sciences

1 Elements and their combinations

account for all the varied types of

matter in the world As a basis for

understanding this concept:

1.a. Students know that during

chemical reactions the atoms in the

reactants rearrange to form products

with different properties.

1.c. Students know metals have

properties in common, such as high

electrical and thermal conductivity

Some metals, such as aluminum (Al),

iron (Fe), nickel (Ni), copper (Cu),

silver (Ag), and gold (Au), are pure

elements; others, such as steel and

brass, are composed of a combination

of elemental metals.

1.f. Students know differences in

chemical and physical properties

of substances are used to separate mixtures and identify compounds.

1.g. Students know properties of solid,

liquid, and gaseous substances, such

as sugar (C6H12O6), water (H2O), helium (He), oxygen (O2), nitrogen (N2), and carbon dioxide (CO2)

ISBN 0-328-23567-9

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by Carmen Padilla

Physical Sciences

chemical change

chemical equation

condensation

evaporation

physical change

product

reactant

sublimation

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ISBN: 0-328-23567-9

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1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06

by Carmen Padilla

How does matter

change?

Physical Changes

Matter changes all the time A physical change takes place

when matter changes in size, shape, volume, or state

For example, a block of ice melts to form a puddle The ice

and puddle are different in size, shape, volume, and state Yet

they are the same substance: water A physical change has

taken place

You can cause a physical change by cutting paper, grating

cheese, boiling water, even styling your hair In each case, the

substance stays the same

This tree is made of copper wire Shaping the wire into

a tree caused a physical change.

3

Chemical Changes

A chemical change takes place when one kind of matter

changes into a different kind of matter with different properties

Chemical changes often take place when you prepare meals For example, cooked eggs have different chemical properties than raw eggs Similarly, eggs change to different substances as your body digests them One kind of matter changes into a different kind of matter with different properties

Chemical changes often produce heat, sound, or light But

it isn’t always obvious when a chemical change has taken place

Sometimes you have to look for clues Iron is usually gray When

it rusts, it has a reddish-orange color This indicates a chemical change The rust has different properties than the iron

The copper tree is placed

in a liquid.

Silver crystals formed on the copper tree Chemical changes took place in the liquid and on the copper.

States of Matter

If you leave a glass of lemonade outside on a hot sunny day,

you will soon have less lemonade That’s because lemonade is

mostly water The liquid water will evaporate, turning into a gas

Solid, liquid, and gas are three forms of matter An object’s

state of matter depends on the positions and motions of its

atoms or molecules The position of these particles is different in

each phase of matter

Solids

Solids have a defi nite shape and volume Particles in solids

are usually very close together Forces between the particles

keep them from moving from one place to another Yet solid

particles are not absolutely still They move in place, like a

person in a rocking chair

Particles of air spread far apart in this balloon.

4

5

Liquids

Suppose you try to build a snowman indoors The snow melts into a liquid You don’t have a snowman—you have a mess!

As a solid absorbs heat energy, it melts into a liquid As the solid warms, its particles no longer vibrate in place They begin to move and fl ow past one another That’s why liquids

do not have a shape of their own They take the shape of their container But liquids do have a defi nite volume Forces between liquid particles keep them close together, although not as close

as forces between solid particles

Gases

Particles in gases are very far apart compared with particles

in solids or liquids Gas particles can be squeezed much more than solid or liquid particles That’s because there is so much more space between them

Suppose that you blow up a balloon Gas particles spread out evenly throughout the balloon The balloon is tight and round As the balloon loses air, it is less tight and starts to get smaller The remaining gas particles are still spread out evenly throughout the balloon But the shape and volume of the balloon have changed Like all gases, the air inside the balloon has neither a defi nite shape nor a defi nite volume

Freezing and Melting

When the temperature is 0ºC, freshwater changes It freezes

to become ice Ice also changes state at 0ºC Ice melts to become

water Because 0ºC is the temperature at

which water freezes and melts, 0ºC is

both the freezing point and melting point

of water

Each substance—water, sugar,

gold, and so on—has its own melting

temperature This physical property of

matter is important Chemists can use it

to help them identify a material Engineers

can use it to help them choose the best

materials for automotive parts

Substances have a wide range of melting

temperatures For example, frozen oxygen has a

melting temperature of –218ºC By comparison,

the melting temperature of iron is 1535ºC!

The freezing and melting

temperature is an important

property of a substance.

7

Particles on the Move

Particles move differently in a solid, a liquid, and a gas

The speed with which particles move depends partly on the temperature of a material As temperature increases, particles move faster As temperature decreases, particles move more slowly When liquids get so cold that they freeze solid, their particles slow down and vibrate in place

The faster particles move, the greater the space between the particles becomes As the space between particles increases, matter gets a little larger It expands Particles never get cold enough to stop vibrating—even when a liquid freezes solid

Wet clothes on a line are dried by evaporation.

8

Evaporation

Evaporation takes place when particles leave a liquid and

become a gas You’ve seen it happen if you have ever heated

water to make instant soup or cocoa

Most evaporation takes place at the surface of a liquid

This means that liquid particles change to gas at the surface

Below the surface, the particles stay

liquid If you heat water to the boiling

point, you’ll see the whole liquid full

of gas bubbles

Each liquid has its own boiling

point You can use this physical

property to help identify a liquid

Bubbles rising to the top of the liquid become a gas.

Condensation

Condensation is a process that occurs when a gas turns

into a liquid You can see the results on a glass of ice water

When air particles touch the cold surface of the glass, their temperature falls As they cool, the gas particles condense into liquid droplets on the outside of the glass

Clouds and dew are formed by condensation So are things like fog on a car windshield or on someone’s eyeglasses

Sublimation

Sublimation occurs when a solid changes directly to a gas

without fi rst becoming a liquid The particles move so fast that they escape, as a gas, from the surface of the solid Only some solids undergo sublimation Ice is one that does

When you leave an ice cube in your freezer for a long time, the ice cube shrinks Part of the ice cube changes into water vapor Sublimation has taken place

A more dramatic example is dry ice (solid carbon dioxide) If you expose dry ice to the air, it will change to vapor right before your eyes People who design movie or theater sets use dry ice to create fog

Dry ice can change directly to vapor.

9

A battery

provides

the energy

for the

reaction.

Test tubes collect gas bubbles.

10

Chemical Reactions

There are many types of chemical reactions Each type

produces a chemical change in matter One substance changes

into a different substance with different properties

The picture shows the chemical reaction that takes place

if you run electricity through water Water is the reactant, the

substance used in the chemical reaction Hydrogen and oxygen

are the products, the substances made by the reaction.

During the reaction, water undergoes a chemical change

The atoms in the water molecules rearrange to form hydrogen

and oxygen gases

+

A chemical equation is a sentence that uses symbols to

describe a chemical reaction The chemical equation for the reaction shown on page 10 is shown below

Notice that the reactant, water, is listed on the left side of the equation The products, hydrogen and oxygen, are listed on the right side The arrow is like the equal sign in a math equation

Chemical reactions begin and end with the same amount

of matter They follow a law called the Law of Conservation

of Mass According to that law, the total mass of the reactants equals the total mass of the products

Several chemical reactions take place in fi reworks as they explode in the sky.

11

Three Types of Reactions

Three types of reactions are decomposition reactions,

combination reactions, and replacement reactions The

experiment on page 10 is a decomposition reaction In this type of

reaction, compounds break apart to form smaller compounds

or elements In the experiment, water breaks apart to form

hydrogen and oxygen gases

In a combination reaction, elements or compounds are

combined They come together to form new compounds A

combination reaction takes place when magnesium and oxygen

join to form magnesium oxide A combination reaction also

occurs when iron and sulfur combine to form iron sulfi de

Oxygen and magnesium join

in a combination reaction

The product is magnesium oxide This product has properties that differ from those of the reactants.

12

Na

O N

O N

Ag

Cl Na

13

In a replacement reaction, one or more compounds breaks

apart The parts then switch places

Silver nitrate is chemical used in the fi lm for cameras

Sodium chloride is just plain table salt A replacement reaction takes place when you combine the two chemicals Both of these chemicals are clear liquids in solution When you mix them together, they react to form silver chloride and sodium nitrate

Silver chloride is a solid It will turn the beaker cloudy and eventually settle to the bottom

Notice that the silver (Ag) and sodium (Na) switch places

On the left side of the equation, silver comes fi rst On the right side, sodium comes fi rst

Silver nitrate and sodium chloride undergo a replacement reaction when combined in solution Solid silver chloride forms.

More About Chemical Reactions

Remember that matter can change in two ways: physically

and chemically Chemical changes take place during chemical

reactions Atoms in the reactants rearrange to form products

that have different properties

The chart on page 15 shows how atoms are rearranged

in the three types of chemical reactions you have read about

Find the model of a combination reaction in the chart It

shows what happens when pairs of reactants combine to form

a single product

A candle undergoes both

physical and chemical

changes as it burns.

Decomposition Combination Replacement

Type of Reaction Model

15

Think about the combination reaction that forms carbon dioxide The green circle in the model represents carbon

The purple circle represents oxygen When these substances combine, they form a new substance made up of both kinds of circles The new substance is carbon dioxide

Look at the second row in the chart It shows how atoms rearranged in the decomposition reaction from page 10, where electricity was run through water Look at the third row to see the replacement reaction that causes solid silver chloride to form when you mix silver nitrate and sodium chloride in solution

Remember that no atoms are lost or added in any type of chemical reaction.The atoms simply combine in new ways to form new substances

Using Chemical

Properties

Separating Mixtures

The substances in some

mixtures, like oil and vinegar, have

different physical properties Those

substances can be easily separated

by physical means Other mixtures

cannot easily be separated by physical

means To separate them, a knowledge of

chemical properties is helpful

Scientists use chemical properties to get fossils out of

limestone Vinegar dissolves limestone but does not harm the

fossil itself

Chemical properties are also used to make decaffeinated

coffee Many adults like the taste of coffee but do not like to

have caffeine So coffee manufacturers use chemicals to dissolve

the caffeine in coffee beans

Separating Metals from Ores

Ores are rocks that include metals combined with other

substances Copper ore contains copper Iron ore contains iron

An ore called bauxite contains aluminum Chemical properties

are used to release metals from their ores Iron is separated from

iron ore, copper is separated from copper ore, and bauxite is

changed to aluminum metal

17

Separating Solutions

Chemical properties are also used to separate elements from solutions For example, scientists can use their knowledge about lead to separate it from a solution of water and other materials

Look at the picture The solution being poured is made up

of water, lead, and other materials The solution on the bottom

is made with iodine When the two solutions mix, a reaction takes place The lead solution and the iodine solution combine

to form lead iodide This yellow solid can be easily fi ltered out

of the liquid

Lead solution

Lead iodide

Iodine solution