Lesson 1 Changes of State - SharpSchool...
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Lesson 1 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? Changes of State 52 ENGAGE PS.5 Describe the properties and behavior of water in its solid, liquid, and gaseous phases (states) (PS-M-A5) Also covers PS.12 A
Transcript of Lesson 1 Changes of State - SharpSchool...
Lesson 1
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?
Changes of State
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52ENGAGE
PS.5 Describe the properties and behavior of water in its solid, liquid, and gaseous phases (states) (PS-M-A5)Also covers PS.12A
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What happens when ice melts?
Form a HypothesisWhat 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.
Record the mass of the cup of ice water. Do you think the mass will change as the water warms?
Observe Swirl the ice and water gently for 15 seconds. Record the temperature of the ice water. Next, place the cup under a lamp.
Repeat step 3 every 3 minutes until you have 5 readings after the ice has fully melted.
Record the mass of the cup of water again.
Draw Conclusions
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 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.
• plastic or paper cup
• cool water
• ice cubes
• balance with setof masses
• watch or clock
• thermometer
• lamp
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53EXPLORE
SI.4 Design, predict outcomes, and conduct experiments to answer guiding questions (SI-M-A2) SI.12 Use data and information gathered to develop an explanation 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
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Changes of State
How can matter change state?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.
As heat is absorbed, particles move faster and become less organized. Does a gas gain heat when it condenses?
Clue: Look at the movement of particles.
solid liquid gas
temperature
evaporatemelt
condensefreeze
▶ Essential Question How does matter change when energy is added or removed?
▶ Vocabularyphysical 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
Fact Opinion
▶ Technology e-Glossary, e-Review, and animations online at www.macmillanmh.com
PS.5
Read a Diagram
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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).
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.
▲ Water vapor from the air condensed into liquid water on the surface of these cans.
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?
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▶
▶
When does matter
change states?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 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.
Once the particles are separated, they can move around and increase in temperature again.
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.
Which takes more heat—melting a sample of water or boiling it?
Clue: How long are the levels in the graph for melting and boiling?
solid solid and
liquid
liquid liquid and gas gas
solid
liquid
gas
Absorbed Heat
Temperature in ˚C
meltingpoint
boiling point
Heating Curve for Water
Watch
changes of state at www.macmillanmh.com
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Changes of State for Some Common Materials
Name Melting Point Boiling Point
Copper 1,083°C 2,567°C
Nitrogen -210°C -196°C
Water 0°C 100°C
Table salt 801°C 1,465°C
Iron 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.
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?
Evaporation and
Condensation
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?
SI.16
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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.
The particles in ice are more spread out than the particles in liquid water. This is why ice floats.
liquid water
solid water
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Think, Talk, and WriteVocabulary 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.
Fact 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 A solid.B liquid.C gas.D none of the above.
Test Prep What happens as water changes from a liquid to a gas?A sublimationB evaporationC condensationD freezing
Essential Question How does matter change when energy is added or removed?
Visual Summary
Make a Study GuideMake a layered -look book. Use the titles shown. Summarize what you learned in each topic.
-Review Summaries and quizzes online at www.macmillanmh.com
Adding or removing heat causes matter to go through changes of state.
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.
Descriptive vs. Explanatory WritingWrite 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?
BoilingIt 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?
Math Link M.7Writing Link SI.10
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Inquiry Skill: Use VariablesParticles 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 ItWhen 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.
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▶ Try ItMaterials 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)
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