Lesson 1
Changes
of State
If all the ice in the world melted, the oceans
would rise by more than 65 meters (215 feet)!
This iceberg is melting in Paraiso Bay, Antarctica.
What happens to ice when it melts?
52
ENGAGE
PS.5 Describe the properties and behavior of water in its solid, liquid, and gaseous
phases (states) (PS-M-A5)
A
Also covers PS.12
What happens when ice melts?
Materials
Form a Hypothesis
What happens to the temperature of a cup of ice cubes
and water as the ice melts? Write your answer in the
form “If a cup of ice and water is steadily warmed, then
the temperature of the ice water will....”
Test Your Prediction
Measure Half-fill a cup with cool water, and add
four ice cubes.
• plastic or paper cup
Record the mass of the cup of ice water. Do you
think the mass will change as the water warms?
• cool water
• ice cubes
Observe Swirl the ice and water gently for
• balance with set
of masses
15 seconds. Record the temperature of the ice
water. Next, place the cup under a lamp.
• watch or clock
Repeat step 3 every 3 minutes until you have
5 readings after the ice has fully melted.
• thermometer
• lamp
Record the mass of the cup of water again.
Draw Conclusions
Step
Use your data to make a graph of the
temperature of water versus time.
Interpret Data Describe the temperature
and the mass of the ice water as the ice melted.
Communicate Did your observations support
your prediction? Write a report that describes
whether your prediction was correct.
Explore More
Step
How would the temperature of water change with
time as it freezes? Write a hypothesis and design
an experiment to test it. Conduct your experiment,
and report your findings.
SI.4 Design, predict outcomes, and conduct experiments
tto answer guiding questions (SI-M-A2) SI.12 Use data
a information gathered to develop an explanation
and
of experimental results (SI-M-A4) SI.19 Communicate
ideas in a variety of ways (e.g., … graphs …) (SI-M-A7)
Also covers SI.6, SI.22
53
EXPLORE
How can matter change state?
▶ Essential Question
How does matter change
when energy is added or
removed? PS.5
▶ Vocabulary
physical change, p. 54
evaporation, p. 55
condensation, p. 55
sublimation, p. 55
melting point, p. 56
boiling point, p. 56
freezing point, p. 57
▶ Reading Skill
Fact and Opinion
Opinion
Fact
▶ Technology
e-Glossary, e-Review, and
animations online
at www.macmillanmh.com
What changes when you sharpen a pencil? Does
it stay a pencil? Yes. You only change how the
pencil is shaped, not the type of elements inside. A
physical change alters the form of an object without
changing what type of matter it is. Sharpening your
pencil is an example of a physical change.
Remember there are three common states of
matter: solid, liquid, and gas. The states of matter are
physical properties. If you put a chip of ice on the
kitchen counter, it will melt into a puddle. Overnight,
the puddle is likely to disappear as the water turns
into a gas. These are both physical changes. What
makes water go through changes of state like these?
As you know, particles in objects move around.
In solids, particles only vibrate and are very close
together. In liquids, particles vibrate as they move
past one another and are more spread out. In gases,
particles move quickly and are even more spread out.
The average movement of particles in an object is
measured by its temperature. Changes in temperature
occur when an object gains or loses heat.
Changes of State
condense
freeze
liquid
solid
gas
evaporate
melt
temperature
As heat is absorbed,
particles move faster and
become less organized.
Read a Diagram
Does a gas gain heat when it condenses?
Clue: Look at the movement of particles.
54
EXPLAIN
Heat is the flow of energy between
objects with different temperatures. Heat
can cause water and other matter to change
states, or phases. If a solid gains enough heat,
its particles start moving too fast to stay
together. The solid then changes into a liquid.
If you place an ice cube in a warm place, it
will melt into liquid water. What happens
if you add more heat to a liquid? The
molecules gain energy and escape the liquid’s
surface. The added energy causes the liquid
water to become a gas called water vapor.
The slow change from a liquid to a gas is
called evaporation (ih•va•puh•RAY•shun).
▲ Water vapor from the air
condensed into liquid water
on the surface of these cans.
The opposite happens when heat is
removed from liquid water. Particles lose
energy, slow down, and group together.
Gases lose heat and condense into liquids.
Condensation (kun•den•SAY•shun) occurs
when a gas changes to a liquid. Liquids lose
heat and freeze into solids.
Some solid substances skip the liquid
state of matter when turning into gas.
Sublimation (suh•bluh•MAY•shun) is the
change of state directly from solid into gas.
A substance called dry ice can sublimate at
room temperature. Water can also sublimate.
The frost in a freezer comes from gaseous
water sublimating out of uncovered food or
ice cubes. The gaseous water from the frozen
food condenses on the cold freezer walls to
make the frost.
Water exists in solid form in glaciers and
icecaps, in gas form as water vapor, and in
liquid form in rivers and oceans. Energy from
the Sun can cause the liquid water on Earth’s
surface to evaporate into water vapor. As
the water vapor rises, it cools and condenses
into a liquid. Eventually the water falls back
to the ground as rain, sleet, or snow. This
process is known as the water cycle.
▲ Dry ice, made of carbon and
oxygen, sublimates at room
temperature.
Quick Check
Fact and Opinion Frost can
form in freezers, so it is better
to buy a frost-free freezer.
Which part of this statement is
fact and which part is opinion?
Critical Thinking How could
snow disappear without
making a puddle?
55
EXPLAIN
When does matter
change states?
Once the particles are separated, they
can move around and increase in
temperature again.
We put ice in drinks to keep them
cold. However, ice does not keep drinks
cool just because it is cold. It keeps
drinks cool mainly by melting! How
can melting ice keep things cool? Ice
absorbs heat from the liquid drink.
This heat changes the state of the ice
instead of raising its temperature.
The diagram below is called a
heating curve for water. It shows what
happens to water when heat is steadily
supplied, starting with ice. Do you
see that water melts at 0°C (32°F)
and boils at 100°C (212°F)? The
temperature at which a substance melts
is called its melting point. The melting
point of water is 0°C. Similarly, the
temperature at which a substance boils
is called its boiling point. The boiling
point of water is 100°C. Recall that
the melting point and boiling point of
substances do not depend on mass.
The temperature of water does
not rise while it is melting or boiling.
How can the water absorb heat and
not get hotter? Usually adding heat
to a substance causes the particles
to increase in temperature. During a
change of state, however, heat moves the
particles farther apart from one another.
Read a Diagram
Heating Curve for Water
Clue: How long are the levels in
the graph for melting and boiling?
solid
liquid
boiling ▶
point
Which takes more heat—melting
a sample of water or boiling it?
Watch
changes of state at
gas
www.macmillanmh.com
Temperature
in ˚C
melting
▶
point
solid
solid
and
liquid
liquid
liquid and gas
Absorbed Heat
56
EXPLAIN
gas
Changes of State for Some
Common Materials
Name
Copper
Nitrogen
Water
Table salt
Iron
Melting Point
Boiling Point
1,083°C
2,567°C
-210°C
-196°C
0°C
100°C
801°C
1,465°C
1,538°C
2,861°C
What happens as you remove heat
from water? You follow a cooling
curve. It is just the heating curve in
reverse. The water condenses at the
boiling point and freezes at the melting
point. The temperature at which a
substance freezes is its freezing point.
Every pure substance melts and boils
at specific temperatures. A material with
high melting and boiling points has
particles that are attracted strongly to
one another. A material with low melting
and boiling points has particles that are
weakly attracted to one another. Many
metals will not melt until they reach very
high temperatures. Nonmetal gases will
not condense unless they are very cold.
The temperature in a liquid is the
average energy of the particles within
it. However some particles have slightly
more or less energy than the average.
Particles with more energy can escape
the surface of the liquid and become a
gas. Recall that the slow change from
liquid to gas at temperatures well below
the boiling point is evaporation. It is
always happening. Liquids cool as they
evaporate because their highest energy
particles are leaving.
Evaporation and
Condensation SI.16
Pour an equal amount
of water into two petri
dishes.
Predict Place one
petri dish under
a lamp or in a
sunny place. Put
the other in a cooler or
darker place. Predict which
will evaporate first.
Infer Why did one
dish of water
evaporate first?
Predict Pour an equal amount of
water into two beakers. Add three
ice cubes to each beaker. Cover
both beakers with plastic wrap.
Put one of the beakers under a
lamp or in a sunny place. Put the
other in a cooler or darker place.
Predict which will form condensation
on the plastic wrap first.
Infer Why did the water condense
in one beaker first?
Quick Check
Fact and Opinion Your friend
says ice in a soda keeps the drink
cool but makes it taste bad. Which
part of that statement is fact, and
which part is opinion? Explain.
Critical Thinking Some people
take steam baths to relax. Why
does steam feel hot when it
condenses on your skin?
57
EXPLAIN
How is water different
from other kinds of
matter?
Have you ever wondered why ice cubes
float in a glass of water? Water that freezes
on a lake also floats. Even huge icebergs
float in the ocean. Ice floats in liquid water
because of its density.
Generally, particles draw closer together
as they lose heat. As particles get closer, the
density of a material increases. A material
is usually denser as a solid than as a liquid.
However, water is different from other
kinds of matter. Like other liquids, as
water cools the molecules lose energy and
pack tightly together. However, just before
freezing, water molecules move farther
apart and line up in a solid arrangement.
This arrangement causes molecules to
take up more space when water is a solid
than they do when water is a liquid. When
the water molecules freeze, there is space
between them. For this reason, ice is less
dense than liquid water.
▲ Water is denser as a liquid
than as a solid.
Quick Check
Fact and Opinion Water is less
dense as a solid than as a liquid.
Is this a fact or an opinion?
Critical Thinking What would
happen if you put a plastic bottle
filled with liquid water in the
freezer? Explain.
solid water
liquid water
58
EXPLAIN
The particles in ice are more spread
out than the particles in liquid water.
This is why ice floats.
Visual Summary
Think, Talk, and Write
Adding or removing
heat causes matter to
go through changes of
state.
Vocabulary The temperature at which
a substance melts is called its
.
Fact and Opinion Is it a bad idea
to put a glass bottle full of water in a
freezer? Support your opinion with facts.
Melting and boiling
points vary among
pure substances. Water
melts at 0°C and boils
at 100°C.
Water is different from
other kinds of matter
because it is denser as
a liquid than as a solid.
Make a
Study Guide
Opinion
Critical Thinking Why wouldn’t
turning up the heat on the stove make
boiling water cook things faster?
Test Prep In general, the state of
matter with the most energy is
solid.
liquid.
gas.
none of the above.
A
B
C
D
Test Prep What happens as water
changes from a liquid to a gas?
A sublimation
B evaporation
C condensation
D freezing
Make a layered -look
book. Use the
titles shown.
Summarize
what you learned
in each topic.
Writing Link
Fact
Essential Question How does matter
change when energy is added or
removed?
SI.10
Math Link
M.7
Descriptive vs. Explanatory Writing
Boiling
Write a description about a glass of ice
water. Then write an explanation of what
happens when water changes from liquid
to solid. How are the two styles of writing
different?
It takes about 2,260 joules of heat to
completely boil a gram of water into
a gas. How much heat will it take to
completely boil 5.5 g of water?
-Review Summaries and quizzes online at www.macmillanmh.com
59
EVALUATE
Inquiry Skill: Use Variables
Particles in hot liquids move faster than those in cold
liquids. Since hot water has more energy to get rid of before
it freezes, it shouldn’t freeze as fast as cold water.
That’s what many people thought. But scientists wanted
to know for sure, so they did a series of experiments and
recorded their observations. In these experiments the
scientists changed only one thing at a time. That way they
knew what caused the outcome they observed. What they
changed is called the independent variable. They learned
that sometimes hot water freezes faster than cold
water. This is called the Mpemba effect.
▶ Learn It
When you use variables, you change one
thing at a time to see how it affects the
outcome of the experiment. The thing you
change is the independent variable. The
outcome is the dependent variable. The way
the dependent variable changes depends on
the way the independent variable changes.
For this experiment the independent
variable is the starting temperature of the
water. The time it takes the water to freeze
is the dependent variable. You will change the
starting temperature of the water and record
how this affects the time it takes the water
to freeze.
60
EXTEND
▶ Try It
Materials hot water, cold water, plastic
cups, thermometer, labels,
graduated cylinder, freezer
Make a table like the one shown below
to record your data.
Fill a cup with 120 milliliters of hot
water. Label it Hot Water. Fill a cup
with 120 mL of cold water. Label it Cold
Water. Fill a cup with 80 mL cold and
40 mL hot water. Label it Cool Water.
Fill a cup with 80 mL hot and 40 mL
cold water. Label it Warm Water. Using
the same amount of water in each cup
(120 mL) is a controlled variable.
Record the temperature of each cup
of water on your table. This is the
independent variable.
Place all the cups in a freezer at the
same time. The cups should be close
together and on the same level.
Check the freezer every 10 minutes.
Record when the water in each cup
starts to freeze. Record when the water
in each cup is completely frozen. These
are both dependent variables.
▶ Apply It
Which water froze first: cold, cool,
warm, or hot water? Repeat the
experiment to confirm your findings.
Scientists changed the independent
variable to learn about the Mpemba
effect. What did you learn from your
results? Do you agree that the Mpemba
effect occurs?
What do you think would happen if you
used icy or even hotter water? Are you
still changing the same independent
variable? Use variables and record
data about the investigation. Use the
data to help you develop an opinion
about how water freezes.
SI.5 Identify independent variables, dependent variables, and variables that should
be controlled in designing an experiment (SI-M-A2) SI.7 Record observations using
methods that complement investigations (e.g., journals, tables, charts) (SI-M-A3)
SI.22 Use evidence and observations to explain and communicate the results of
investigations (SI-M-A7)
61
EXTEND