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Thermodynamics
Estimated Time of Duration
1.5 Hours
Objectives
- Familiarize the students with the concepts of pressure and temperature
- Demonstrate the relationship between pressure and temperature
- Familiarize the students with the difference between solids, liquids, and gases
Materials
| Description | Quantity |
|---|---|
| Gas Apparatus | 3 |
| 2 liter beaker (boil H2O, ice water, hot H2O) | 3 |
| 1 liter Dewer (LN2) | 2 |
| 400 ml beakers for t-couple ice baths | 7 |
| Ice Tongs (for handling material in LN2) | 1 |
| Gloves (for cold stuff) | 1 pair |
| Copper Wire (4 ft./t-couple, 30 t-couples) | 2 feet per person |
| Constantan Wire (2 ft./t-couple, 30 t-couples) | 1 foot per person |
| Steel Wool | 4-6 pieces |
| Hot plates | 2 |
| Bicycle Pump | 1 |
| Alligator leads and clips | 6 |
| Volt Meters | 3 |
| MacIntosh Computers with Cricket Graph | 2-3 |
| Printer (might need to network the printer) | 1 |
| Wire Cutters | 1 pair |
| Styrofoam Cooler (for ice) | 1 |
| Ice | 1 bag |
| Liquid Nitrogen (in container) | 2-4 liters |
| Calculators | enough For demonstrations |
| Bananas | 2-3 |
| Wood Plank and nails | 1 |
| Rose or Carnation (opened) | 2 |
| styrofoam cup | 1 ea. |
Room Preparation
- Set up the three stations following the numbers in the student handout. Each station will need:
- Voltmeter
- 400 ml beaker with ice water bath
- Temperature Baths: there are 3 required temperature baths:
- Liquid Nitrogen. Use a 2 liter beaker with water at room temperature
- Ice Water. Use a 2 liter beaker with water and ice.
- Boiling Water. use a 2 liter beaker and a hot plate to boil the water
- Gas Flasks: each flask must be filled to the same initial pressure at room temperature
- Bicycle pump
- Use the bicycle pump to pressurize your flask to 20 PSI. Place your flask in your temperature bath.
- Have two pieces of copper wire and one piece of Constantan cut and ready to go (about 2 ft. of each should do) for each group.
- Have a beaker of ice water ready for demonstrating the thermocouple.
- Determine the atmospheric pressure for the day in torr (mm Hg).
- Make sure the computer(s) are on and ready to go. Check the printer.
Lesson
Liquid Nitrogen/Gas
- Dump some Liquid N2 on the floor (to get things rolling...)
- Reminds you of Water and Steam.
- What is the relationship between steam and water?
- When you heat water (a liquid) up enough, it turns into a steam (a gas). What happens to steam when it cools down again?
- It condenses into a liquid
- Introduce it as Liquid N2 The same can be done with Nitrogen, a very common gas in the air we breath. If you cool it down enough, it will turn into a liquid.
- Point out that it is evaporating into a gas
- Liquid Nitrogen is very cold Carnation experiment - Get a volunteer...
- What is a gas?
Pressure
- What is pressure?
- It's basically how hard gas presses against its surroundings
- What causes the pressure of a gas to change? PV=nRT
- What is atmospheric pressure?
- Gas weighs something Atmospheric pressure is the weight off all the air above us on our head and shoulders
- How do we measure pressure?
- Talk about reading our gauges
Formulas
- What is a formula?
- How do we use them?
- Explain how graphs and computers can give us formulas... x vs. y, plot an example from a formula Scientists take data, then work backwards... Computer will do all the hard work for us...
Units
- Celsius temperature scale, and pressures in Torr
- How would you measure the length of something?
- Inches, feet, miles, centimeters, meters, kilometers (for example)
- Kelvin (Celsius+273) is to Fahrenheit, and Torr is to PSI, as centimeters is to inches and kilometers is to miles.
Measuring Temperatures (for younger students)
- We know the temperature of Liquid Nitrogen, Ice Water and Boiling Water.
- TLN2 = TICE = 0°C = 273 K TBOIL = 100°C = 373 K
Measuring temperatures with thermocouples (for more mature students)
- How do thermocouples work?
- We use thermocouples because normal thermometers do not measure such low temperatures They are based upon the fact that two different but touching metals create a small current. This current changes as the temperature changes. By recording the voltage, we can estimate the temperature.The attached table of voltages and temperatures can be referenced in the lesson.
- Hand out wires and construct a thermocouple with them Take a copper wires and wrap the end of one around one of the ends of the Constantan wire together. Do the same with the other end of the Constantan wire. The open ends of the two Copper wires are attached to the volt meter. One of the twists goes in the fluid you're measuring the temperature of, while the other twist goes into ice water (for a reference temperature).
- Demonstrate how they work
- Experiment
- Split up group into 4 groups.
- Each group goes to one of four stations, where they read the temperature and pressure.
- Upon reading that data, move on to the next station.
- When all four stations have been visited, go to the computer table, enter the data on Cricket Graph.
- Create graph and curve fit with a SIMPLE curve
- Print out at Printer.
- Come together and share the formula for pressure and temperature. Using the pressure for station #4, estimate the temperature.
- Measure temperature
- Talk about any error that may occur.