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) 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. 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. plastic or paper cup cool water ice cubes balance with set of masses watch or clock thermometer lamp 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. Step Step 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 53 EXPLORE
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 Fact Opinion Technology e-glossary, e-review, and animations online at www.macmillanmh.com 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. Changes of State freeze condense solid liquid gas melt evaporate 54 EXPLAIN As heat is absorbed, particles move faster and become less organized. temperature Read a Diagram Does a gas gain heat when it condenses? Clue: Look at the movement of particles.
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. Water vapor from the air condensed into liquid water on the surface of these cans. 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? 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. Heating Curve for Water boiling point solid liquid gas 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. Read a Diagram 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? Watch changes of state at www.macmillanmh.com Temperature in C melting point solid solid and liquid liquid liquid and gas gas Absorbed Heat 56 EXPLAIN
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. 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? Quick Check SI.16 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? 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 Make a Study Guide Make a layered -look book. Use the titles shown. Summarize what you learned in each topic. 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. Think, Talk, and Write 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. 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 sublimation B evaporation C condensation D freezing Essential Question How does matter change when energy is added or removed? Writing Link SI.10 Math Link M.7 Descriptive vs. Explanatory Writing 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? Boiling 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