Junior Science Heat
By the end of this lesson you should be able to • OP22: understand that heat is a form of energy and that it can be converted into other forms of energy • OP23: investigate and describe the expansion of solids, liquids and gases when heated, and contraction when cooled • OP24: demonstrate the expansion of water on freezing • OP25: measure the temperature of various solids and liquids at, above and below room temperature; determine the melting point of ice and the boiling point of water • OP26: investigate the effect of pressure on the boiling point of water • OP27: explain the difference between heat and temperature • OP28: carry out experiments that involve changes of state from • solid to liquid and liquid to solid • liquid to gas and gas to liquid • OP29: plot a cooling curve and explain the shape of the curve in terms of latent heat
OP22: understand that heat is a form of energy • Side-arm flask, plastic drinking cup, heat source, pointed support for cup. • Place the side arm flask containing water on the hotplate and let the water boil.
The cup is on a sharp point, e.g. a pencil or the holder of a compass needle. • Steam coming from the side arm of spins the cup into which little vanes have been cut. • Remove the source of heat. The water stops boiling, the steam stops - the cup stops spinning. • This shows heat energy being converted to kinetic energy.
Hero's engine About 100 B.C., a Greek inventor known as Hero of Alexandria came up with a new invention that depended on the mechanical interaction of heat and water. He invented a rocket-like device called an aeolipile. It used steam for propulsion.
Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas travelled through the pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate. This showed that heat was a form of energy.
Expansion contraction - topics for class discussion • Why are there lines of tar in footpaths and concrete walls? • How are metal rings put so tightly around barrels and wooden wheels? • Why are there gaps in railway tracks? • Why are telephone wires loosely strung on the poles? • How does an automatic fire sprinkler system work? • Why does a thick glass tumbler crack if boiling water is added to it, whereas one made of thin glass does not?
Expansion contraction - topics for class discussion • Why are bottles of lemonade, etc. not filled completely to the top? • Why are we told not to throw aerosol cans into the fire? • Why is it dangerous to open the radiator cap in a car while the engine is still hot? • Why do water pipes sometimes burst in cold weather? • How does a Galileo thermometer work?
OP24: demonstrate the expansion of water on freezing • Dramatic on-screen Quicktime movie of an ice bomb, from the Journal of chemical education.
OP25 • measure the temperature of various solids and liquids at, above and below room temperature; determine the melting point of ice and the boiling point of water
OP26: investigate the effect of pressure on the boiling point of water
OP28: • show change of state fromsolid to liquid and liquid to solidliquid to gas and gas to liquid
OP29: plot cooling curve and explain the shape of the curve in terms of latent heat The temperature of a tube of water was recorded every 30 seconds as it cooled from an initial temperature of 22°C
The small container for the water can be made using a plastic pipette dropper. Cut off the dropping end, three-quarter fill with water and insert the temperature probe.
As the water cools, the temperature drops As the temperature drops, the energy of the particles in the substance reduces. The particles start to join together. As the particles join together, bonds are formed. When bonds are formed, heat is given out; this heat stops the temperature falling further so while the liquid is changing to solid, there is no further decrease in temperature. . Supercooling - particles haven’t got organised to form crystals yet Eventually, all the water turns to ice, no more particles join together, so now the temperature can continue to drop Completely cool !