A D V A N C E D P H Y S I C S C O U R S E C H A P T E R 7 : THE R M O D Y N A M I C S

Transcription

1 A D V A N C E D P H Y S I C S C O U R S E C H A P T E R 7 : THE R M O D Y N A M I C S FOR HIGH SCHOOL PHYSICS CURRICULUM AND ALSO THE PREPARATION OF ACT, DSST, AND AP EXAMS This is a complete video-based high school physics course that includes videos, labs, and hands-on learning. You can use it as your core high school physics curriculum, or as a college-level test prep course. Either way, you ll find that this course will not only guide you through every step preparing for college and advanced placement exams in the field of physics, but also give you in hands-on lab practice so you have a full and complete education in physics. Includes text reading, exercises, lab worksheets, homework and answer keys. BY AURORA LIPPER SUPERCHARGED SCIENCE Supercharged Science Page 1

2 TABLE OF CONTENTS Material List... 3 introduction... 4 Thermal Physics Introduction... 5 Temperature... 6 Absolute Zero... 7 Thermometers... 8 Thermal Energy... 9 The Human Body Changing Molecular Speeds States of Matter Melting and Evaporation Condensation and Freezing What are clouds? Changing States at Unusual Places Heat Heat goes from hot to cold Heat Capacity Specific Heat Capacity Fire Water Balloon How much energy does a candy bar have? Heat Flow Heat and States of Matter Sublimation Heat Energy of a Peanut Thermostat Triple Point Conduction Convection Convection Currents Radiation Calorimeter Heat Engines Hero Engine Stirling Engine Ideal Gas Law Homeowrk Problems with Solutions Supercharged Science Page 2

3 MATERIAL LIST While you can do the entire course entirely on paper, it s not really recommended since physics is based in realworld observations and experiments! Here s the list of materials you need in order to complete all the experiments in this unit. Please note: you do not have to do ALL the experiments in the course to have an outstanding science education. Simply pick and choose the ones you have the interest, time and budget for. alcohol burner or candle with adult help balloons black spray paint bottles of water (2) candles CDs (3 old ones) chemistry stand with glass test tube and holder coin drill with 1/16 bit electrical tape electrical wire (3- conductor solid wire) fire extinguisher fishing line (15lb. test or similar) foil wrapper (from stick of gum or candy bar) food coloring freezer ice cubes incandescent light (or sunlight) index cards matches or lighter (and adult help) mug with hot water nylon bushing (from hardware store) old inner tube from a bike wheel pack of steel wool paper clip paper, one sheet of each: white and black penny pepper permanent marker plastic bottle plastic syringe push pin raw peanuts razor rubbing alcohol scissors silver highlighter (or aluminum foil) silver or white spray paint small pliers soda bottle (2L) soda can (4) solar drinking bird super glue and instant dry Swiss army knife (with can opener option) tape thermal paper ( Liquid Crystal Sheet see website for ordering information) wire cutters 2017 Supercharged Science Page 3

4 INTRODUCTION If you put an ice cube in a glass of lemonade, the ice cube melts. The thermal energy from your lemonade moves to the ice cube. Increasing the temperature of the ice cube and decreasing the temperature of your lemonade. The movement of thermal energy is called heat. The ice cube receives heat from your lemonade. Your lemonade gives heat to the ice cube. Heat can only move from an object of higher temperature to an object of lower temperature. We re going to learn about temperature, heat energy, atoms, matter, phase changes, and more in our unit on Thermodynamics as we build steam boats, fire-water balloons, hero engines, thermostats, Stirling engines, and more! Does this sound familiar? I m too cold. Get me a sweater! This soup s too hot! Phew, I m sweating. Yowtch, that pan handle burned me! If you ve ever made any of the above comments, then you were talking about thermal energy. Very clever of you, don t you think? Thermal energy is basically the energy of the molecules moving inside something. The faster the molecules are moving, the more thermal energy that something has. The slower they are moving, the less thermal energy that something has. I m sure at some point you ve said, Wow, my internal thermal energy is way high! I need a liquid with a low thermal energy. What you ve never said that?! Oh, wait. I bet it sounded like this when you said it, Wow, I m hot! I need a cool drink. Whenever we talk about the temperature of something we are talking about its thermal energy. Objects whose molecules are moving very quickly are said to have high thermal energy or high temperature. The higher the temperature, the faster the molecules are moving. You may remember that temperature is just a speedometer for molecules. You may have asked yourself the question, So, if everything is made of molecules, and these molecules are often speeding up and slowing down what happens to the stuff these molecules are are made of if they change speed a lot? Will my kitchen table start vibrating across the room if the table somehow gets too hot? No, it s pretty unlikely that your table will begin jumping around the room, no matter how hot it gets. However, some interesting things do happen when molecules change speeds Supercharged Science Page 4

5 THERMAL PHYSICS INTRODUCTION Here s a teleclass to get you started on learning about Thermodynamics. The next set of lessons will take you in more detail on each topic covered in the teleclass (and more)! 2017 Supercharged Science Page 5

6 TEMPERATURE Temperature is a way of talking about, measuring, and comparing the thermal energy of objects. We use three different kinds of scales to measure temperature. Fahrenheit, Celsius, and Kelvin. (The fourth, Rankine, which is the absolute scale for Fahrenheit, is the one you ll learn about in college.) Mr. Fahrenheit, way back when (18th century) created a scale using a mercury thermometer to measure temperature. He marked 0 as the temperature ice melts in a tub of salt. (Ice melts at lower temperatures when it sits in salt. This is why we salt our driveways to get rid of ice). To standardize the higher point of his scale, he used the body temperature of his wife, 96. As you can tell, this wasn t the most precise or useful measuring device. I can just imagine Mr. Fahrenheit, Hmmm, something cold something cold. I got it! Ice in salt. Good, okay there s zero, excellent. Now, for something hot. Ummm, my wife! She always feels warm. Perfect, 96. I hope he never tried to make a thermometer when she had a fever. Just kidding, I m sure he was very precise and careful, but it does seem kind of weird. Over time, the scale was made more precise and today body temperature is usually around 98.6 F. Later, (still 18th century) Mr. Celsius came along and created his scale. He decided that he was going to use water as his standard. He chose the temperature that water freezes at as his 0 mark. He chose the temperature that water boils at as his 100 mark. From there, he put in 100 evenly spaced lines and a thermometer was born. Last but not least Mr. Kelvin came along and wanted to create another scale. He said, I want my zero to be ZERO! So he chose absolute zero to be the zero on his scale Supercharged Science Page 6

7 ABSOLUTE ZERO Absolute zero is the theoretical temperature where molecules and atoms stop moving. They do not vibrate, jiggle or anything at absolute zero. In Celsius, absolute zero is -273 C. In Fahrenheit, absolute zero is -459 F (or 0 R). It doesn t get colder than that! 2017 Supercharged Science Page 7

8 THERMOMETERS As you can see, creating the temperature scales was really rather arbitrary: I think 0 is when water freezes with salt. I think it s just when water freezes. Oh, yea, well I think it s when atoms stop! Many of our measuring systems started rather arbitrarily and then, due to standardization over time, became the systems we use today. So that s how temperature is measured, but what is temperature measuring? 2017 Supercharged Science Page 8

9 THERMAL ENERGY Temperature is measuring thermal energy which is how fast the molecules in something are vibrating and moving. The higher the temperature something has, the faster the molecules are moving. Water at 34 F has molecules moving much more slowly than water at 150 F. Temperature is really a molecular speedometer. When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren t moving quite so fast Supercharged Science Page 9

10 THE HUMAN BODY Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are! Let s test this out now with three different cups of water (I colored mine in the video so you could tell which is which): Objects whose molecules are moving very quickly are said to have high thermal energy or high temperature. The higher the temperature, the faster the molecules are moving. You may remember that temperature is just a speedometer for molecules Supercharged Science Page 10

11 Sensing Temperature Overview: Have you ever wondered how an ice-cold glass of water gets water drops on the outside of the cup? It s all about temperature change! You will see how a temperature difference can fool your fingers in today s hot and cold experiment. What to Learn: You will understand why condensation occurs and feel how skin can detect a temperature difference, but not an exact temperature. Materials cup of hot water cup of cold water cup of room-temperature water Experiment 1. Place one finger from one hand in the hot (not scalding) water. Place a finger from your other hand in the ice-cold water. Leave them there for a moment. 2. At the same time, take both fingers and place them in the room-temperature water. What do you feel? 3. Complete the data table. Sensing Temperature Data Table What do your fingers feel? Write your observations here! Right Hand Finger Left Hand Finger Observations Reading Have you ever wondered how an ice-cold glass of water gets water drops on the outside of the cup? Where does that water come from? Does it ease its way through the glass? Did someone come by and squirt the glass with water? No, of course not. Some of the gaseous water molecules in the air came close enough to the cold glass to lose some molecular 2017 Supercharged Science Page 11

12 speed. Since they lost speed, they formed bonds between each other and liquefied. They condensed on the cold surface of the glass. Imagine, though, if you will, that you live several hundred years ago and the process of condensation wasn t understood. You happen to be an inquisitive, highly perceptive, person (which of course you are) and you notice this film of water showing up on cold things. Water appearing out of apparently nowhere! You d be pretty amazed, wouldn t you?!? Isn t it amazing that every time you pick up a cold can of soda there are molecular interactions happening right in front of your eyes! This is why science is so wonderful. It provides the skills to see these amazing things and the skills to investigate and perhaps understand them. The skin contains temperature sensors that work by detecting the direction heat flows in or out of the body, but not temperature directly. These sensors change temperature depending on their surroundings. When one finger is heated up then placed in water at room temperature, the heat flows out of the body. The brain gets a message saying the finger is cooler. A finger placed in ice water followed by room temperature water tells the brain it was detecting a heat flow into your body and presto! You have one confused brain. In order for heat to flow, there must be a temperature difference. But why then do the metal legs of a table feel colder than the wood tabletop when both are at the same room temperature? The metal will feel colder because heat flows away from your skin faster into the metal than the wood. We ll talk about heat capacity in a later experiment, but this is why scientists had to invent the thermometer: The human body isn t designed to detect temperature, only heat flow. Exercises 1. How did the hot finger feel when it was placed into the room-temperature water? 2. How did the cold finger feel when it was placed into the room-temperature water? 2017 Supercharged Science Page 12

13 3. Based on your observations, what can you infer about how a skin detects temperature? 4. After taking a hot shower, a student noticed something interesting. When she put on her glasses and went into the hallway, her glasses fogged up with tiny droplets of water. What was happening? 2017 Supercharged Science Page 13

14 Answers to Exercises 1. How did the hot finger feel when it was placed into the room temperature water? (cold) 2. How did the cold finger feel when it was placed into the room temperature water? (hot) 3. Based on your observations, what can you infer about how a skin detects temperature? (The skin detects temperature change but not the actual temperature.) 4. After taking a hot shower, a student noticed something interesting. When she put on her glasses and went into the hallway, her glasses fogged up with tiny droplets of water. What was happening? (When she took her warm glasses into the colder hallway, the air around her glasses cooled off, causing the air to change to drops of liquid water.) 2017 Supercharged Science Page 14

15 CHANGING MOLECULAR SPEEDS You may have asked yourself the question, So, if everything is made of molecules, and these molecules are often speeding up and slowing down what happens to the stuff these molecules are made of if they change speed a lot? Will my kitchen table start vibrating across the room if the table somehow gets too hot? No, it s pretty unlikely that your table will begin jumping around the room, no matter how hot it gets. However, some interesting things do happen when molecules change speeds Supercharged Science Page 15

16 STATES OF MATTER Matter has a tendency to hang out in fairly stable states under normal temperatures. There are three common states of matter; solid, liquid, and gas. How many states of matter do you see in this video with the balloon? If you want to do this experiment on the stove, heat a glass bottle in a saucepan (use about an inch of water in the pot and make sure there s water both inside and outside the bottle). There is another state of matter called plasma but it is not common on Earth. Plasma is a highly energized gas. It is used in florescent lights. I m going to assume you know a bit about solids, liquids and gasses so I won t go into much detail about them here (see Unit 3 and Unit 8 for more information) Supercharged Science Page 16

17 Balloon gymnastics Overview: Heat causes all kinds of things to happen. We ll zoom in on the micro scale of molecules as we explore in today s lesson. What to Learn: Heat energy influences all kinds of observable phenomena on our planet. Materials water plastic bottle balloon stove top and saucepan or the setup in the video Lab Time 1. Pour a couple of inches of water into an empty soda bottle and cap with a 7-9 balloon. You can secure the balloon to the bottle mouth with a strip of tape if you want, but it usually seals tight with just the balloon itself. 2. Fill a saucepan with an inch or two of water, and add your bottle. Heat the saucepan over the stove with adult help, keeping a close eye on it. Turn off the heat when your balloon starts to inflate. Since water has a high heat capacity, the water will heat before the bottle melts. (Don t believe me? Try the Fire-Water Balloon Experiment first to see how water conducts heat away from the bottle!) 3. When you re finished, stick the whole thing in the freezer for an hour. What happened to the balloon? 4. Record all observations in the worksheet Balloon Gymnastics Observations 1. What happens to the balloon when the balloon is heated? What is happening to its air molecules? 2. What happens to the balloon when you put it in the freezer? What is happening with its molecules now? 2017 Supercharged Science Page 17

18 Reading This material may be helpful to interpret today s experiment: Is it warmer upstairs or downstairs? The upstairs in a house is warmer because the pockets of warm air rise because they are less dense than cool air. The more the molecules move around, the more room they need, and the further they get spaced out. Think of a swimming pool and a piece of aluminum foil. If you place a sheet of foil in the pool, it floats. If you take the foil and crumple it up, it sinks. The more compactly you squish the molecules together, the denser it becomes. As for why mountains and valleys are opposite, it has to do with the Earth being a big massive ball of warm rock which heats up the lower atmosphere in addition to winds blowing on mountains and changes in pressure as you gain altitude in a nutshell, it s complicated! What s important to remember is that the Earth system is a lot bigger than our bottle-saucepan experiment, and can t be represented in this way. Exercises Answer the questions below: 1. Draw a group of molecules at a very cold temperature in the space below. Use circles to represent each molecule. 2. True or False: A molecule that heats up will move faster. a. True b. False 3. True or False: A material will be less dense at lower temperatures. a. True b. False 2017 Supercharged Science Page 18

19 Answers to Exercises: Balloon Gymnastics 1. Draw a group of molecules at a very cold temperature in the space below. Use circles to represent each molecule. (should be grouped very tightly) 2. True or False: A molecule that heats up will move faster (true) 3. True or False: A material will be less dense at lower temperatures (false) 2017 Supercharged Science Page 19

20 MELTING AND EVAPORATION What I do want to talk about is what happens as temperatures change in a substance. Let s take one of the neatest substances on the Earth, water. Water is quite special since it can be in its solid, liquid and gas state at relatively normal temperatures. It s quite special for a variety of other reasons too, but we ll leave it at that for now. Pretend we have an ice cube on a frying pan (poor ice cube). Right now the water is in a solid state. It s holding its shape. The molecules in the water are held together by strong, stiff bonds. These bonds hold the water molecules in a tight, very specific pattern called a matrix. This matrix holds the water molecules in a crystalline pattern and the solid water holds its shape. Now, let s turn on the heat. The heat is transferred from the stove to the frying pan to the ice cube. (We ll talk about heat transfer a bit later.) As the ice cube absorbs the heat the molecules begin to vibrate faster (the temperature is increasing). When the molecules vibrate at a certain speed (gain enough thermal energy) they stretch those strong, stiff bonds enough that the bonds become more like rubber bands or springs. When the bonds loosen up, the water loosens up and becomes liquid. There are still bonds between the molecules, but they are a bit loose, allowing the molecules to move and flow around each other. The act of changing from a solid to a liquid is called melting. The temperature at which a substance changes from a solid to a liquid is called its melting point. For water, that point is 32 F or 0 C. Now we will watch carefully as our ice cube continues to melt (little is more exciting than watching an ice cube melt golf maybe). A bit after we see our ice cube go from solid to completely liquid, we notice bubbling. What s going on now? If we were able to see the molecules of water at this point we d be quite amazed at the fantastic scene before us. At 212 F or 100 C water goes from a liquid state to a gaseous state. This means that the loosey goosey bonds that connected the molecules before have been stretched as far as they go, can t hold on any longer and POW! they snap. Those water molecules no longer have any bonds and are free to roam aimlessly around the room. Gas molecules move at very quick speeds as they bounce, jiggle, crash and zip around any container they are in. The act of changing from a liquid to a gas is called evaporation or boiling and the temperature at which a substance changes from a liquid to a gas is called its boiling point. This is a really cool experiment that shows you how to make clouds indoors (there s a second experiment that uses a bike pump watch that one also!): 2017 Supercharged Science Page 20

21 Indoor Rain Clouds Overview: Today you get to vaporize liquid oceans of molecules and make it rain when the rising cloud decks hit the coldness of space. Sound like fun? What to Learn: The movement of atmospheres on different planets is affected by the temperature of the planet and the molecules in the atmosphere. Materials Glass of ice water Glass of hot water Towel Ruler Experiment 1. Please be careful with this lab! The hot water can burn you! 2. Take two clear glasses that fit snugly together when stacked. (Cylindrical glasses with straight sides work well.) 3. Fill one glass half-full with ice water and the other half-full with very hot water (definitely an adult job and take care not to shatter the glass with the hot water!). Be sure to leave enough air space for the clouds to form in the hot glass. 4. Place the cold glass directly on top of the hot glass and wait several minutes. If the seal holds between the glasses, a rain cloud will form just below the bottom of the cold glass, and it actually rains inside the glass! (You can use a damp towel around the rim to help make a better seal if needed.) 5. Complete the data table. Measure the water height carefully with your ruler. If you have 2 of water in the hot water glass, then write 2. Please be careful when measuring hot water! 2017 Supercharged Science Page 21

22 Indoor Rain Clouds Data Table Hot Water Height Ice Water Height How well did it rain? Reading This experiment demonstrates state changes of matter. When hot vapor rises (like from the hot core of a gaseous planet) and hits a cold front (like the coldness of outer space in the upper atmosphere), the vapor condenses into liquid drops and rains, or can even freeze solid into ice chunks. Neptune and Uranus both have methane ice in their upper atmospheres. Both Jupiter and Saturn have upper cloud decks of water vapor and clouds of ammonia. The water vapor clouds are right at the freezing temperature of water. Questions to Answer 1. Which combination made it rain the best? Why did this work? 2017 Supercharged Science Page 22

23 2. Draw your experimental diagram, labeling the different components: 3. Add in labels for the different phases of matter. Can you identify all three states of matter in your experiment? 2017 Supercharged Science Page 23

24 Answers to Exercises: Indoor Rain Clouds 1. Which combination made it rain the best? Why did this work? (The greater the temperature difference, the better this experiment will work. The more water you have, the less the temperature will fluctuate for each glass, thus making it able to rain for longer periods of time.) 2. Draw your experimental diagram here, labeling the different components: 3. Add in labels for the different phases of matter. Can you identify all three states of matter in your experiment? (Ice = solid; water = liquid, gas between two glasses is water vapor, nitrogen, and oxygen.) 2017 Supercharged Science Page 24

25 CONDENSATION AND FREEZING I don t know about you, but I think it s getting a bit hot in here. Let s turn the heat down a bit and see what happens. If our gaseous water molecules get close to something cool, they will combine and turn from gaseous to liquid state. This is what happens to your bathroom mirror during a shower or bath. The gaseous water molecules that are having fun bouncing and jiggling around the bathroom get close to the mirror. The mirror is colder than the air. As the gas molecules get close they slow down due to loss of temperature. If they slow enough, they form loosey goosey bonds with other gas molecules and change from gas to liquid state. Here s a cool trick magicians use when they open the freezer The act of changing from gas to liquid is called condensation. The temperature at which molecules change from a gas to a liquid is called the condensation point Supercharged Science Page 25

26 Ghost coin Overview: This spooky idea takes almost no time, requires a dime and a bottle, and has the potential for creating quite a stir in your next magic show. The idea is basically this: when you place a coin on a bottle, it starts dancing around. But there s more to this trick than meets the scientist s eye. What to Learn: Heat energy is carried through different substances and affects the properties of different types of matter Materials Coin Freezer Plastic bottle (not glass) Lab Time 1. Remove the cap of an empty plastic water or soda bottle and replace it with a dime. 2. Stick the whole thing upright in the freezer overnight. Make sure your group s bottle is labeled! First thing in the morning, take it out and set it on the table. What happens? 3. Record all observations in the worksheet. Ghost Coin Observations Draw a picture of the water molecules inside of the water bottle when this experiment begins Supercharged Science Page 26

27 Now draw a picture of what they look like in the morning. What happened? 2017 Supercharged Science Page 27

28 Reading Matter has a tendency to hang out in fairly stable states under normal temperatures. There are three common states of matter; solid, liquid, and gas. There is another state of matter called plasma, but it is not common on Earth. Plasma is a highly energized gas. It is used in fluorescent lights. I m going to assume you know a bit about solids, liquids and gases so I won t go into much detail about them here (see Unit 3 and 8 for more information). What I do want to talk about is what happens as temperatures change in a substance. Let s take one of the neatest substances on the Earth, water. Water is quite special since it can be in its solid, liquid and gas state at relatively normal temperatures. It s quite special for a variety of other reasons, too, but we ll leave it at that for now. Pretend we have an ice cube on a frying pan (poor ice cube). Right now the water is in a solid state. It s holding its shape. The molecules in the water are held together by strong, stiff bonds. These bonds hold the water molecules in a tight, very specific pattern called a matrix. This matrix holds the water molecules in a crystalline pattern and the solid water holds its shape. Now, let s turn on the heat. The heat is transferred from the stove to the frying pan to the ice cube. (We ll talk about heat transfer a bit later.) As the ice cube absorbs the heat, the molecules begin to vibrate faster (the temperature is increasing). When the molecules vibrate at a certain speed (gain enough thermal energy) they stretch those strong, stiff bonds enough that the bonds become more like rubber bands or springs. When the bonds loosen up, the water loosens up and becomes liquid. There are still bonds between the molecules, but they are a bit loose, allowing the molecules to move and flow around each other. The act of changing from a solid to a liquid is called melting. The temperature at which a substance changes from a solid to a liquid is called its melting point. For water, that point is 32 F or 0 C. Now we will watch carefully as our ice cube continues to melt (little is more exciting than watching an ice cube melt golf, maybe). A bit after we see our ice cube go from solid to completely liquid, we notice bubbling. What s going on now? If we were able to see the molecules of water at this point we d be quite amazed at the fantastic scene before us. At 212 F or 100 C water goes from a liquid state to a gaseous state. This means that the loosey goosey bonds that connected the molecules before have been stretched as far as they go, can t hold on any longer and POW! they snap. Those water molecules no longer have any bonds and are free to roam aimlessly around the room. Gas molecules move at very quick speeds as they bounce, jiggle, crash and zip around any container they are in. The act of changing from a liquid to a gas is called evaporation or boiling, and the temperature at which a substance changes from a liquid to a gas is called its boiling point. I don t know about you, but I think it s getting a bit hot in here. Let s turn the heat down a bit and see what happens. If our gaseous water molecules get close to something cool, they will combine and turn from gaseous to liquid state. This is what happens to your bathroom mirror during a shower or bath. The gaseous water molecules that are having fun bouncing and jiggling around the bathroom get close to the mirror. The mirror is colder than the air. As the gas molecules get close, they slow down due to loss of temperature. If they slow enough, they form loosey goosey bonds with other gas molecules and change from gas to liquid state. The act of changing from gas to liquid is called condensation. The temperature at which molecules change from a gas to a liquid is called the condensation point. Clouds are made of hundreds of billions of tiny little droplets of liquid water that have condensed onto particles of some sort of dust. Now let s turn the heat down a bit more and see what happens. As the temperature drops and the molecules continue to slow, the bonds between the molecules can pull them together tighter and tighter. Eventually the molecules will fall into a matrix, a pattern, and stick 2017 Supercharged Science Page 28

29 together quite tightly. This would be the solid state. The act of changing from a liquid to a solid is called freezing, and the temperature at which it changes is called (say it with me now) freezing point. Think about this for a second is the freezing point and melting point of an object at the same temperature? Does something go from solid to liquid or from liquid to solid at the same temperature? If you said yes, you re right! The freezing point of water and the melting point of water are both 32 F or 0 C. The temperature is the same. It just depends on whether it is getting hotter or colder as to whether the water is freezing or melting. The boiling and condensation point is also the same point. Now I m going to mess things up a little bit. Substances can change state at temperatures other than their different freezing or boiling points. Many liquids change from liquid to gas and from gas to liquid relatively easily at room temperatures. And, believe it or not, solids can change to liquids and even gases and vice versa at temperatures other than the usual melting, freezing, or boiling points. So what s the point of the points? At a substance s boiling, freezing, etc, points, all of the substance must change to the next state. The condition of the bonds cannot remain the same at that temperature. For example, at 100 C water must change from a liquid to a gas. That is the speed limit of liquid water molecules. At 100 C the liquid bonds can no longer hold on and all the molecules convert to gas. Exercises Answer the questions below: 1. When a gas turns into a liquid, this is called: a. Convection b. Conduction c. Absorption d. Condensation 2. When water boils, what happens to the bonds between its molecules? 2017 Supercharged Science Page 29

30 3. What is the best way to describe how the bonds between water molecules behave when in a liquid state? a. Solid bridges b. Rubber bands c. No bonds d. Brittle like chalk 4. The crystalline shape of a solid is referred to as: a. a matrix b. a vortex c. a crystal d. a cube 2017 Supercharged Science Page 30

31 Answers to Exercises: Ghost Coin 1. When a gas turns into a liquid, this is called: (condensation) 2. When water boils, what happens to the bonds between its molecules? (They snap or break.) 3. What is the best way to describe how the bonds between water molecules behave when in a liquid state? (rubber bands or elastic) 4. The crystalline shape of a solid is referred to as: (a matrix) 2017 Supercharged Science Page 31

32 WHAT ARE CLOUDS? Clouds are made of hundreds of billions of tiny little droplets of liquid water that have condensed onto particles of some sort of dust. Now let s turn the heat down a bit more and see what happens. As the temperature drops and the molecules continue to slow, the bonds between the molecules can pull them together tighter and tighter. Eventually the molecules will fall into a matrix, a pattern, and stick together quite tightly. This would be the solid state. The act of changing from a liquid to a solid is called freezing and the temperature at which it changes is called (say it with me now) freezing point. Think about this for a second is the freezing point and melting point of an object at the same temperature? Does something go from solid to liquid or from liquid to solid at the same temperature? If you said yes, you re right! The freezing point of water and the melting point of water are both 32 F or 0 C. The temperature is the same. It just depends on whether it is getting hotter or colder as to whether the water is freezing or melting. The boiling and condensation point is also the same point. Now I m going to mess things up a little bit. Substances can change state at temperatures other than their different freezing or boiling points. Many liquids change from liquid to gas and from gas to liquid relatively easily at room temperatures. And, believe it or not, solids can change to liquids and even gases and vice versa at temperatures other than the usual melting, freezing, or boiling points. So what s the point of the points? 2017 Supercharged Science Page 32

33 CHANGING STATES AT UNUSUAL PLACES At a substance s boiling, freezing, etc, points, all of the substance must change to the next state. The condition of the bonds cannot remain the same at that temperature. For example, at 100 C water must change from a liquid to a gas. That is the speed limit of liquid water molecules. At 100 C the liquid bonds can no longer hold on and all the molecules convert to gas Supercharged Science Page 33

34 HEAT Believe it or not, the concept of heat is really a bit tricky. What we call heat in common language, is really not what heat is as far as physics goes. Heat, in a way, doesn t exist. Nothing has heat. Things can have a temperature. They can have a thermal energy but they can t have heat. Heat is really the transfer of thermal energy. Or, in other words, the movement of thermal energy from one object to another. If you put an ice cube in a glass of lemonade, the ice cube melts. The thermal energy from your lemonade moves to the ice cube. Increasing the temperature of the ice cube and decreasing the temperature of your lemonade. The movement of thermal energy is called heat. The ice cube receives heat from your lemonade. Your lemonade gives heat to the ice cube. Heat can only move from an object of higher temperature to an object of lower temperature Supercharged Science Page 34

35 HEAT GOES FROM HOT TO COLD Coffee cools down and ice water heats up. That s one of the laws of thermodynamics. Do you remember what temperature is? Temperature measures how fast molecules are moving, right? Well, when heat transfers (moves) from one object to another, the movement of the molecules in the higher temperature object slow down and the movement of the molecules in the lower temperature object speed up. The liquid crystal sheet is temperature-sensitive. When the sheet received heat from the bulb, the temperature goes up and changes color. The plastic sheets remain black except for the temperature range in which they display a series of colors that reflect the actual temperature of the crystal. Here s a neat experiment that uses this type of special thermal paper and a silver highlighter: 2017 Supercharged Science Page 35

36 HEAT CAPACITY Now let s take explore how, even though heat can move from one object to another, it doesn t necessarily mean that the temperature of the objects will change. You may ask, What? Heat can move from one object to another without temperature changing one little bit?!?! We re going to take a look at one of the ways heat can move while the thermometer doesn t. When things change phase (change from solid to liquid or liquid to gas or well, you get the picture) the temperature of those objects don t change. If you were able to take the temperature of water as it changed from a solid (ice) to a liquid you would notice that the temperature of that piece of ice will stay at about 32 F until that piece of ice was completely melted. The temperature would not increase at all. Even if that ice was in an oven, the temperature would stay the same. Once all the solid ice had disappeared, then you would see the temperature of the puddle of water increase. By the way, as the ice is melting, from where is heat being transferred? Heat is being transferred, by conduction, from the air. One key distinction is that objects don t contain heat, but they contain energy. Heat is the transfer of energy from from one object to another, or from one system to another, like a hot cup of coffee to the cool ambient air. Heat can change the temperature of objects when it transfers the energy. In the example with the coffee cup, it lowered the temperature of the coffee. Imagine putting a sponge under a slowly running faucet. The sponge would continue to fill with water until it reached a certain point and then water started to drip from it. You could say that the sponge had a water capacity. It could hold so much water before it couldn t hold any more and the water started dripping out. Heat capacity is how much heat an object can absorb before it increases in temperature. It s often used interchangeably with specific heat capacity, but in reality it s a little different Supercharged Science Page 36

37 SPECIFIC HEAT CAPACITY Specific heat capacity is how much heat energy a mass of a material must absorb before it increases 1 C. It s how much heat is needed to raise the temperature of 1 gram of the material. Heat Capacity is how much heat is required to raise the temperature. The units of heat capacity are J per Kelvin, whereas for specific heat capacity, the units are J per (gram-k). Each material has its own specific heat. The higher a material s specific heat, the more heat it must absorb before it increases in temperature. Water is unique in that it has a very large specific heat. Liquid water s specific heat is over 4 which is very high. In comparison, granite is 0.8, aluminum is 0.9, rubbing alcohol is 2.4 and gold is 0.1. To get the same amount of rubbing alcohol and liquid water to increase the same amount of temperature, you would need to pump about twice the amount of heat into the water. To get the same amount of gold and liquid water to increase the same amount of temperature, you would need to pump 40 times the amount of heat into the water! 2017 Supercharged Science Page 37

38 FIRE WATER BALLOON In other words, it takes more energy to heat water then it does to heat alcohol, gold, or for that matter most other things. Here s a cool experiment you can do to really bring this idea alive that uses only water, a balloon, and a lit candle: Have you ever dipped a toe in the largest body of water on the planet the Pacific Ocean? If you have, you know it s colder than you d expect, especially if it s summer warm outside. It s for two reasons, both of which are related to the heat energy equation: 2017 Supercharged Science Page 38

39 Fire water balloon Overview: Heat energy can be observed in many ways. This simple experiment allows us to see how heat is transferred. What to Learn: We re exploring how heat energy can move between objects in a variety of ways. Materials Balloon Water Matches, candle, and adult help Sink Lab Time 1. Put the balloon under the faucet and fill the balloon with some water. 2. Now blow up the balloon and tie it, leaving the water in the balloon. You should have an inflated balloon with a tablespoon or two of water at the bottom of it. 3. Carefully light the match or candle and hold it under the part of the balloon where there is water. 4. Feel free to hold it there for a couple of seconds. You might want to do this over a sink or outside just in case! 5. Record observations in the worksheet below Fire-Water Balloon Observations 1. What did the water do to the heat of the match? 2. Why didn t the balloon pop? What does this tell you about heat energy in this system? 2017 Supercharged Science Page 39

40 So why didn t the balloon pop? The water absorbed the heat! The water actually absorbed the heat coming from the match so that the rubber of the balloon couldn t heat up enough to melt and pop the balloon. Water is very good at absorbing heat without increasing in temperature, which is why it is used in car radiators and nuclear power plants. Whenever someone wants to keep something from getting too hot, they will often use water to absorb the heat. Think of a dry sponge. Now imagine putting that sponge under a slowly running faucet. The sponge would continue to fill with water until it reached a certain point and then water started to drip from it. You could say that the sponge had a water capacity. It could only hold so much water before it couldn t hold any more and the water started dripping out. Heat capacity is similar. Heat capacity is how much heat an object can absorb before it increases in temperature. This is also referred to as specific heat. Specific heat is how much heat energy a mass of a material must absorb before it increases 1 C. Reading If you ve ever had a shot, you know how cold your arm feels when the nurse swipes it with a pad of alcohol. What happened there? Well, alcohol is a liquid with a fairly low boiling point. In other words, it goes from liquid to gas at a fairly low temperature. The heat from your body is more than enough to make the alcohol evaporate. As the alcohol went from liquid to gas, it sucked heat out of your body. For things to evaporate, they must suck in heat from their surroundings to change state. As the alcohol evaporated, you felt cold where the alcohol was. This is because the alcohol was sucking the heat energy out of that part of your body (heat was being transferred by conduction) and causing that part of your body to decrease in temperature. As things condense (go from gas to liquid state) the opposite happens. Things release heat as they change to a liquid state. The water gas that condenses on your mirror actually increases the temperature of that mirror. This is why steam can be quite dangerous. Not only is it hot to begin with, but if it condenses on your skin it releases even more heat which can give you severe burns. Objects absorb heat when they melt and evaporate/boil. Objects release heat when they freeze and condense. Do you remember when I said that heat and temperature are two different things? Heat is energy it is thermal energy. It can be transferred from one object to another by conduction, convection, and radiation. We re now going to explore heat capacity and specific heat. Water is very good at absorbing heat without increasing in temperature, which is why it is used in car radiators and nuclear power plants. Whenever someone wants to keep something from getting too hot, they will often use water to absorb the heat. Think of a dry sponge. Now imagine putting that sponge under a slowly running faucet. The sponge would continue to fill with water until it reached a certain point and then water started to drip from it. You could say that the sponge had a water capacity. It could only hold so much water before it couldn t hold any more and the water started dripping out. Heat capacity is similar. Heat capacity is how much heat an object can absorb before it increases in temperature. This is also referred to as specific heat. Specific heat is how much heat energy a mass of a material must absorb before it increases 1 C Supercharged Science Page 40

41 Exercises Answer the questions below: 1. What is specific heat? a. The specific amount of heat any object can hold b. The amount of energy required to raise the temperature of an object by 1 degree Celsius. c. The type of heat energy an object emits d. The speed of a compound s molecules at room temperature 2. Name two types of heat energy: 3. What type (or types) of heat energy is at work in today s experiment? 4. True or False: Water is poor at absorbing heat energy. a. True b. False 2017 Supercharged Science Page 41

42 Answers to Exercises: Fire Water Balloon 1. What is specific heat? (the amount of heat energy that material must absorb to increase in temperature 1 degree C) 2. Name two types of heat energy (conduction, convection, and radiation) 3. What type (or types) of heat energy is at work in today s experiment? (radiation and convection) 4. True or False: Water is poor at absorbing heat energy. (false) 2017 Supercharged Science Page 42

43 HOW MUCH ENERGY DOES A CANDY BAR HAVE? How much energy does a candy bar have? How much energy does a candy bar have? If you flip it over and read the nutritional information on the back, you can figure it out with a little help from the video below: 2017 Supercharged Science Page 43

44 HEAT FLOW Let s learn how to calculate the heat flow based solely on temperature readings from a thermometer (this is going to be important later in this lab): 2017 Supercharged Science Page 44

45 HEAT AND STATES OF MATTER Heat can also change the state of matter. When an ice cube melts into a liquid puddle, it remains at the same temperature until the phase change is complete, and only then does the temperature begin to rise, even though heat was added throughout the entire process. The thermometer reading will stay on the same temperature reading until the ice is completely melted Supercharged Science Page 45

46 SUBLIMATION Carbon dioxide goes straight from a solid to a gas, which is called sublimation. It totally skips going through the liquid phase! How do you handle the transition from a solid block to a gas cloud? Here s how: Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy Supercharged Science Page 46

47 HEAT ENERGY OF A PEANUT What makes up a peanut? Inside you ll find a lot of fats (most of them unsaturated) and antioxidants (as much as found in berries). And more than half of all the peanuts Americans eat are produced in Alabama. We re going to learn how to release the energy inside a peanut and how to measure it. Here s what you do. If you don t have the fancy equipment for the experiment, here s a cheaper, easier way to do it using a candle and a paperclip 2017 Supercharged Science Page 47

48 Peanut Energy Overview: Put your safety goggles on for today s lab we ll be looking at fire again. You ll be measuring how much energy a peanut holds by setting it on fire and measuring an increase in water temperature. What to Learn: All our energy needs on earth come from somewhere. We cannot make our own food, but plants can. We are all connected to the plants and soils that they grow in because they provide our very basic needs, as well as some of our more modern needs. Materials Goggles 2 shelled peanuts Small pair of pliers Match or lighter Test tube in wire test tube holders (these look like pliers that are designed to hold a test tube) Scale Thermometer Lab Time 1. Today we re working with fire, so follow all special instructions provided about working with fire today. 2. Measure your test tube on the scale when it s empty: grams 3. Fill up your test tube with about 10 grams of water and weigh it again: grams 4. Measure the initial temperature of the water: oc 5. Put on safety goggles. 6. Using a small pair of pliers, hold the peanut and ask an adult to light the peanut with the lighter until it catches fire. 7. Upon ignition (when the peanut is burning by itself and doesn t need the lighter), hold the peanut under the water close to the bottom of the test tube until the peanut stops burning. 8. Quickly measure the final temperature of the water: oc 9. Record your results on the worksheet. 10. Allow the peanut to cool as you record your observations and complete the data tables Supercharged Science Page 48

49 Let's take an example measurement. Suppose you measured a temperature increase from 20 C to 100 C for 10 grams of water, and boiled off 2 grams. We need to break this problem down into two parts - the first part deals with the temperature increase, and the second deals with the water escaping as vapor. The first basic heat equation is this: Q = m c T Q is the heat flow (in calories) m is the mass of the water (in grams) c is the specific heat of water (which is 1 degree per calorie per gram) and T is the temperature change (in degrees) So our equation becomes: Q = 10 * 1 * 80 = 800 calories. If you measured that we boiled off 2 grams of water, your equation would look like this for heat energy: Q = L m L is the latent heat of vaporization of water (L= 540 calories per gram) m is the mass of the water (in grams) So our equation becomes: Q = 540 * 2 = 1080 calories. The total energy needed is the sum of these two: Reading Q = 800 calories calories = 1880 calories. Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy. Peanuts are part of the bean family, and actually grow underground (not from trees like almonds or walnuts). In addition to your lunchtime sandwich, peanuts are also used in woman's cosmetics, certain plastics, paint dyes, and also when making nitroglycerin. What makes up a peanut? Inside you'll find a lot of fats (most of them unsaturated) and antioxidants (as much as found in berries). And more than half of all the peanuts Americans eat are produced in Alabama. We're going to learn how to release the energy inside a peanut and how to measure it. There's chemical energy stored inside a peanut, which gets transformed into heat energy when you ignite it. This heat flows to raise the water temperature, which you can measure with a thermometer. You should find that your peanut contains calories of energy! Now don't panic - this isn't the same as the number of calories you're allowed to eat in a day. The average person aims to eat around 2,000 Calories (with a capital "C"). 1 Calorie = 1,000 calories. So each peanut contains Calories of energy (the kind you eat in a day). Do you see the difference? So did all the energy from the peanut go straight to the water, or did it leak somewhere else, too? The heat actually warmed up the nearby air, too, but we weren't able to measure that. If you were a food scientist, you'd use a nifty little device known as a bomb calorimeter to measure calorie content. It's basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you'd get Calories of energy from one peanut!) 2017 Supercharged Science Page 49