• During this Investigation, you will learn that heat is a form of kinetic energy which, ultimately, means that heat is the energy of motion.

• Unlike the obvious form of motion involved in dropping a ball or swinging a golf club, the motion involved in the kinetic energy of heat is at the molecular level. Increased heat in a substance causes its constituent molecules to move faster and further.

Note: The molecular motion of atoms and molecules increases the chances of them colliding with each other in chemical reactions. In a similar manner, increasing the kinetic energy of a solution will enhance the solubility of a solute in a solvent. This is why heating speeds up most chemical reactions and heating and stirring a solution promotes solubility.

Note: In this Investigation, you will learn that thermometers work by increased kinetic energy and the consequent expansion of the sealed fluid that results.

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• This slide introduces the concept of kinetic energy in connection with heat.

• Kinetic energy always moves from areas of higher to lower energy.

• Kinetic energy is measure in Joules (J).

Note: The analogy of the cue ball causing the rapid movement of the other pool balls on the break is a good one. Now, try to think in terms of molecules moving.

• Look at the streaking traces of the balls bouncing off each other and the bumpers of the table as a result of the kinetic energy introduced by the cue ball. It is very analogous to the bouncing of molecules off each other and the beaker wall when heating (transferring kinetic energy) a liquid.

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• This slide draws a distinction between heat and temperature.

• Temperature is a measure of kinetic energy in a substance, but not energy itself.

• There are no energy units for temperature. To say a substance has 10^oC of energy, for example, makes no sense at all.

Note: Once again, the relationship between temperature, kinetic energy, and degree of molecular motion is highlighted in this slide.

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• Remember that in slide HEAT-1-2, we stated a Rule that kinetic energy always moves from areas of higher energy to areas of lower energy.

• In this slide, this Rule is restated to say that the transfer of thermal energy (heat) always moves from areas of high temperature to low temperature.

Note: Students sometimes have difficulty with this concept. For example, you may believe that “cold” enters an electric burner when it’s shut off or that “cold” enters your body when they go outside in the winter. Actually, in both cases, the heat/kinetic energy simply moves from areas of higher to lower energy. The burner eventually comes to room temperature so that it is in thermal equilibrium with the air in the room and no net energy transfer occurs. If this happens to our bodies outside, we freeze to death! It’s that simple.

• The Law of Conservation of Energy also states that heat energy, like any other energy, is neither created nor destroyed. The heat from the “cooling” burner doesn’t disappear, it is transferred into the room and increases the air temperature ever so slightly.

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Note: This slide quickly goes over how glass and liquid thermometers work. This is exactly what you will do in the Lab for this Investigation as you calibrate your own thermometer. It is worth pointing out that early physicists calibrated their thermometers in a very similar manner.

• How the liquid inside the thermometer gains energy. When the thermometer is placed into a hot solution, for example, kinetic energy is first transferred from the solution to the glass molecules in the tube until they contain as much kinetic energy as the surrounding solution. This energy is then transferred to the fluid inside the thermometer until it contains as much kinetic energy as the glass and surrounding solution. The fluid molecules inside the thermometer now move faster, expanding the fluid volume and forcing the liquid up in the tube.
• What happens when the liquid inside the thermometer falls? When the solution surrounding the thermometer is cooler than the fluid inside the thermometer or the thermometer is removed from the heated solution and exposed to cooler room temperatures, kinetic energy inside the thermometer decreases. As this happens, the fluid molecules slow down, the liquid contracts, and its level in the thermometer drops.

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• This slide illustrates the relationship between kinetic energy, temperature, and phase transitions.

Note: The labeling on the slide describes the situation that exists at the freezing and boiling point.

Note: Two additional points may be made here:

• You may notice that temperature (y-axis) increases in the solid, liquid, and gas phases but has a momentary plateau exactly at the two-phase transitions (freezing and boiling). As indicated in the text in this slide, both phase transitions involve a rearrangement of the molecules in the sample. Some of the applied kinetic energy/heat is involved in these rearrangements and therefore the temperature stays the same even though the kinetic energy/heat energy changes. This is a good illustration of what was stated earlier – that temperature is only a measurement of energy but not energy itself.

• Notice that in the solid/liquid phase change, the process is referred to as freezing when the kinetic energy drops and as melting when the kinetic energy rises. The reverse of boiling is referred to as condensation (transition from gas to liquid).

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• You must always be cautious when heating glass!

• Goggles should always be worn even when only heating or boiling water because sometimes slight cracks in glassware cause them to break when heated.

Note: A more likely accident occurs if you heat empty glassware. This can occur if a hotplate is turned on and the glassware is placed on it and then you become preoccupied measuring out the volume of liquid to be placed in it. If the glassware gets too hot, it can shatter. Alternatively, students may pour liquid into a very hot piece of glassware with predictable results!

• Always wear goggles when heating glass!