Special Science Teleclass: Thermodynamics

Monday December 1, 2014

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!


You’ll discover how to boil water at room temperature, heat up ice to freeze it, make a fire water balloon, and build a real working steam boat as you learn about heat energy. You’ll also learn about thermal energy, heat capacity, and the laws of thermodynamics.


Materials:


  • cup of ice water
  • cup of room temperature water
  • cup of hot water (not scalding or boiling!)
  • tea light candle and lighter (with adult help)
  • balloon (not inflated)
  • syringe (without the needle)
  • block of foam
  • copper tubing (¼” diameter and 12” long)
  • bathtub or sink
  • scissors or razor
  • fat marker (to be used to wrap things around, not for writing)

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Key Concepts

The terms hot, cold, warm etc. describe what physicists call thermal energy. Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy that object has.


There are three different scales for measuring temperature. Fahrenheit, Celsius and Kelvin. (There’s also a fourth temperature scale for absolute Fahrenheit called Rankine.) Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Your skin, mouth and tongue are antennas which can sense thermal energy.


There are four states of matter: Solid, liquid, gas and plasma. Solids have strong, stiff bonds between molecules that hold the molecules in place. Liquids have loose, stringy bonds between molecules that hold molecules together but allow them some flexibility. Gasses have no bonds between the molecules. Plasma is similar to gas but the molecules are very highly energized. Materials can change from one state to another depending on the temperature and the bonds. Changing from a solid to a liquid is called melting. Changing from a liquid to a gas is called boiling, evaporating, or vaporizing. Changing from a gas to a liquid is called condensation. Changing from a liquid to a solid is called freezing. All materials have given points at which they change from state to state. Melting point is the temperature at which a material changes from solid to liquid.  Boiling point is the temperature at which a material changes from liquid to gas. Condensation point is the temperature at which a material changes from gas to liquid. Freezing point is the temperature at which a material changes from liquid to gas.


What’s Going On?

Heat is the movement of thermal energy from one object to another. Heat can only flow from an object of a higher temperature to an object of a lower temperature (this is the First Law of Thermodynamics). Heat is movement of thermal energy from one object to another. When an object absorbs heat it does not necessarily change temperature.  Objects release heat as they freeze and condense. Objects absorb heat as they evaporate and melt. Freezing points, melting points, boiling points and condensation points are the “speed limits” of the phases. Once the molecules reach that speed they must change state.


Heat capacity is how much heat an object can absorb before its temperature increases. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C. Heat capacity is influenced by the specific heat of the material and/or the amount of the material. Each material has its own specific heat. The higher a material’s specific heat is, the more heat it must absorb before its temperature increases. A larger amount of something will have a higher heat capacity then a smaller amount of something. Water has a very high heat capacity.


Questions:

  1. True or False: Water is poor at absorbing heat energy.
  2. True or False: A molecule that heats up will move faster.
  3. True or False: A material will be less dense at lower temperatures.
  4. For gases, if we increase the temperature, what happens to the pressure and the volume?
  5. What is specific heat?
  6. What is heat?
  7. Does heat flow from cold to hot? Give an example.
  8. What do the our body sense, heat flow or temperature? Are they the same thing?
  9. How can we boil room temperature water without heating up the water?

Answers:


  1. False.
  2. True.
  3. False. (Usually.)
  4. If we increase the temperature, the pressure increases and the volume decreases. This is called the Ideal Gas Law (remember the ping pong balls from the teleclass?)
  5. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.
  6. Heat is the movement of thermal energy from one object to another.
  7. No. Heat flows from hot to cold. (This is the First Law of Thermodynamics.) A hot cup of coffee left out on a cold morning will eventually cool to the surrounding air temperature.
  8. Heat flow. No they are not the same thing. Temperature is a measure of how much energy the molecules have.
  9. By increasing the pressure by decreasing the volume, we can force the bubbles out of the water and it will boil. Boiling is when the liquid water turns into a gas, NOT when the liquid water heats up. Boiling can happen at many different temperatures when you change the pressure.

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Temperature Exercises

Sunday September 5, 2010

Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.


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1. What is thermal energy?


2. What does temperature measure?


3. What are the three different scales used to measure temperature?


4. What is absolute zero?


5. If something is hot, what are its molecules doing?


6. In our “Spread It Around” experiment why did the food coloring spread out faster in the hot bowl than in the cold bowl?


7. In which parts of your body do you have your thermal energy antenna?


8. What are the four states of matter (ignoring BEC)?


9. Which states have no bonds between the molecules?


10. Which state has bonds that hold the molecules in a tight matrix?


11. As the temperature increases, what happens to the bonds that allow a substance to go from solid to liquid?


12. What happens to the bonds as a substance reaches its boiling point?


13. What happens to the bonds as a substance reaches its freezing point?


Need answers?


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Answers to Temperature Exercises

Sunday September 5, 2010

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!


Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.


Answers:
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1. 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.


2. Temperature measures thermal energy. In other words, temperature measures the amount that the molecules are moving. Thermometers are speedometers for molecules.


3. Fahrenheit, Celsius, and Kelvin.


4. Absolute zero is a theoretical temperature where molecules and atoms stop moving. This temperature has never been reached in the laboratory but they have come close.


5. Its molecules are moving very quickly.


6. In the hot bowl, the molecules are moving very fast. Since they are moving quickly, they bump into the food coloring molecules more and harder spreading them out faster than in the cold water.


7. Skin.


8. Solid, liquid, gas, plasma


9. Gases and plasma


10. Solid


11. The bonds are forced to stretch and loosen up since the molecules are moving at greater speeds.


12. As a substance reaches its boiling point it changes from a liquid to a gas. As this happens the bonds that are holding the molecules together break allowing the molecules to wander off on their own as a gas.


13. As a substance reaches its freezing point it turns from a liquid to a solid. The bonds tighten up, pulling the molecules into a matrix and forming a nice solid substance.


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Heat Energy Exercises

Sunday September 5, 2010

Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.


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1. What is heat?


2. Does heat flow from higher to lower temperature, from lower to higher temperature or does it matter?


3. When I first turn on the shower the shower curtain keeps blowing into my legs. Is this an example of conduction, convection or radiation?


4. When I bite into a pizza, the heat is transferred painfully to the roof of my mouth. Is this an example of convection, conduction or radiation?


5. Someone sits a little too close to me on a bus and I can feel the heat coming off of them. Is this an example of convection, conduction or radiation?


6. My daughter holds my hand as we walk across the street. I can feel heat coming from her hand to mine. Is this an example of convection, conduction or radiation?


7. It’s a hot sunny day outside. Am I better off wearing a dark shirt or a light shirt if I want to stay cool?


8. An object’s temperature always drops when it loses heat. True or false?


9. What happens to molecules as they change from one state to another?


10. When objects evaporate do they absorb heat or release heat?


11. Why do we sweat when we’re hot?


12. Why doesn’t temperature change when things are changing state?


13. What is heat capacity?


14. Which would cool down faster, a bottle of maple syrup or a teaspoon of maple syrup?


15. Owww!! I just burned my mouth on a piece of pizza! The strange thing is the crust is just warm. What happened?


16. When I eat at a fast food restaurant I always eat my fries before the burger since the fries get cold so much faster. Which has a higher heat capacity, the fries or the burger?


17. Why do I fill a hot water bottle with hot water and not just hot air?


Need answers?


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Answers to Heat Energy Exercises

Sunday September 5, 2010

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!


Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.


Answers:
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1. Heat is the movement of thermal energy from one object to another.


2. Heat can only flow from a higher temperature object to a lower temperature object.


3. Convection. The heat from the hot water in the shower heats up the air in the shower. The heated air rises. As the heated air rises, it creates a convection current. Which draws air into the shower and blows the shower curtain into my legs. Many of the winds on the Earth are caused by hot air rising and cold air sinking.


4. This is conduction. The fast moving molecules of the pizza bombard my poor mouth molecules. This, in turn, creates sound energy as I scream “OUCH!”.


5. This is radiation. Humans can transfer heat by radiation. The fellow sitting next to me was giving off infra-red radiation.


6. This time it’s primarily conduction. The molecules in her little hand are vibrating quickly and causing my molecules to vibrate quicker as well. There is probably some radiation going on as well, but since our hands are touching her molecules can directly affect my molecules.


7. A light colored shirt reflects more infra-red radiation so I’ll stay cooler.


8. False.


9. The “bonds” between molecules change. They can either tighten up or loosen up depending on whether the energy is increasing or decreasing.


10. They absorb heat.


11. The sweat absorbs excess heat from the body as it evaporates and cools us off.


12. The energy that’s entering the object is being used to change the bonds between the molecules. The molecules have reached their “speed limit”. They can’t go any faster or slower without changing state.


13. Heat capacity is how much heat an object can absorb before its temperature increases.


14. The teaspoon. The smaller the amount the less heat capacity it has.


15. The cheese has a much higher heat capacity then the crust. So the cheese stays hot much longer.


16. The burger holds onto its heat longer then the fries. The burger has a higher heat capacity.


17. Water has a higher heat capacity so it cools much more slowly than air. A hot air bottle will be cool in a matter of seconds.  Hot water will take many minutes to cool down.


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Fire-Water Balloon

Sunday September 5, 2010

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 then 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. Here’s what you do:


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You Need:


  • Balloon
  • Water
  • Matches, candle, and adult help
  • Sink


Download Student Worksheet & Exercises


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!


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 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.


Exercises Answer the questions below:


  1. What is specific heat?
    1. The specific amount of heat any object can hold
    2. The amount of energy required to raise the temperature of an object by 1 degree Celsius.
    3. The type of heat energy an object emits
    4. The speed of a compound’s molecules at room temperature
  2. Name three ways thermal energy can be transferred from one object to another:
  3. At what point does the balloon pop?
  4. True or False: Water is poor at absorbing heat energy.
    1. True
    2. False

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Convection Currents

Sunday September 5, 2010

Every time I’m served a hot bowl of soup or a cup of coffee with cream I love to sit and watch the convection currents. You may look a little silly staring at your soup but give it a try sometime!


Convection is a little more difficult to understand than conduction. Heat is transferred by convection by moving currents of a gas or a liquid. Hot air rises and cold air sinks. It turns out, that hot liquid rises and cold liquid sinks as well.


Room heaters generally work by convection. The heater heats up the air next to it which makes the air rise. As the air rises it pulls more air in to take its place which then heats up that air and makes it rise as well. As the air get close to the ceiling it may cool. The cooler air sinks to the ground and gets pulled back near the heat source. There it heats up again and rises back up.


This movement of heating and cooling air is convection and it can eventually heat an entire room or a pot of soup. This experiment should allow you to see convection currents.


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You need:


  • A pot
  • A stove with adult help
  • Pepper
  • Ice cubes
  • Food Coloring (optional)


1. Fill the pot about half way with water.


2. Put about a teaspoon of pepper into the water.


3. Put the pot on the stove and turn on the stove (be careful please).


4. Watch as the water increases in temperature. You should see the pepper moving. The pepper is moving due to the convection currents. If you look carefully you many notice pepper rising and falling.


5. Put an ice cube into the water and see what happens. You should see the pepper at the top of the water move towards the ice cube and then sink to the bottom of the pot as it is carried by the convection currents.


6. Just for fun, put another ice cube into the water, but this time drop a bit of food coloring on the ice cube. You should see the food coloring sink quickly to the bottom and spread out as it is carried by the convection currents.


Did you see the convection currents? Hot water rising in some areas of the pot and cold water sinking in other areas of the pot carried the pepper and food coloring throughout the pot. This rising and sinking transferred heat through all the water causing the water in the pot to increase in temperature.


Heat was transferred from the flame of the stove to the water by convection. More accurately, heat was transferred from the flame of the stove to the metal of the pot by conduction and then from the metal of the pot throughout the water through convection.


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