Deep Analysis

• Before the glass tube was placed in the boiling water, which had greater kinetic energy the boiling water or the liquid in the glass tube? The boiling water had greater kinetic energy than the liquid in the glass tube. The boiling water was warmer than the liquid in the glass tube.

• What happened to the level of the liquid in the sealed glass tube when it was placed in boiling water? The level of the liquid inside the glass tube was higher after being in the boiling water. As soon as the glass tube was placed in the boiling water, the liquid began to rise in the glass tube. Eventually, the liquid rose to a certain point and then remained there until taken out of the boiling water.

• Before the glass tube was placed in the saltwater ice bath, which had greater kinetic energy, the liquid in the glass tube or the water and ice in the saltwater bath? The saltwater ice bath had lower kinetic energy than the liquid in the glass tube. The saltwater ice bath was colder than the liquid in the glass tube.

• What happened to the level of the liquid in the sealed glass tube when it was placed in the saltwater ice bath? The level of the liquid inside the glass tube was lower after it was placed in a test tube of water that was put into the saltwater ice bath. When the glass tube in a water-filled test tube was placed in the saltwater ice bath, the liquid inside the glass tube moved lower and lower in the tube until a certain point. Eventually, the liquid stopped moving. This occurred after the water in the test tube froze.

• Describe the direction of heat transfer between the boiling water and the liquid in the glass tube in Trial 1. The molecules of boiling water had greater kinetic energy than the molecules of the liquid in the glass tube. (The boiling water was hotter than the room temperature liquid.) Kinetic energy is always transferred from areas of higher kinetic energy to areas of lower kinetic energy. Heat is the transfer of thermal energy, which includes kinetic energy. Therefore, the heat was transferred from the boiling water to the liquid inside the glass tube.

• Describe the direction of heat transfer between the saltwater ice bath and the liquid in the glass tube in Trial 2. The molecules of the liquid inside the glass tube had higher kinetic energy than the molecules in the saltwater ice bath. Kinetic energy is always transferred from areas of higher kinetic energy to areas of lower kinetic energy. Heat is the transfer of thermal energy, which includes kinetic energy. Therefore, the heat was transferred from the liquid inside the glass tube to the liquid and solids in the saltwater ice bath. Students may also suggest that heat was transferred from the surrounding air to the saltwater ice bath because the air around the saltwater ice bath was higher in temperature (greater kinetic energy) than the saltwater ice bath.

Discuss the concepts students have learned thus far. Ask them to answer the Conclusion question.

• Explain why the level of the liquid in the glass tube changed when it was placed in the boiling water and in the saltwater ice bath. Use the terms heat transfer and kinetic energy in your answer. There was a difference in the kinetic energy of the molecules of boiling water and the molecules of liquid inside the glass tube. The molecules in the boiling water had higher kinetic energy than the molecules of liquid in the glass tube. The boiling water was hotter than the liquid in the glass tube. Heat is transferred from areas of higher heat to lower heat. Therefore, the heat was transferred from the molecules of boiling water to molecules of the liquid inside the glass tube. The transfer of heat increased the kinetic energy of the molecules of liquid inside the glass tube. The molecules of the liquid inside the glass tube moved faster and farther apart. As a result, the liquid expanded, rising up the tube. When the glass tube was placed in the saltwater ice bath, the heat was transferred from the molecules of liquid in the glass tube to the molecules in the saltwater ice bath. The transfer of heat into the saltwater ice bath decreased the kinetic energy of the molecules of liquid inside the glass tube. The molecules of the liquid in the glass tube moved more slowly and the distance of each vibration decreased. As a result, the liquid contracted, moving lower down the tube.

• Did you observe any phase changes during Trials 1 and 2? Explain your answer. Yes. During Trial 1 the liquid form of water was in the beaker. As the water boiled, some of the water (liquid) changed into water vapor (gas). During Trial 2, the liquid form of water was in the test tube. As the heat was transferred from the water to the saltwater ice bath, some of the water froze, becoming ice.

Discuss the questions that follow Trials 3 and 4. The questions pertain to the thermometer that students calibrated.

• Which scale did you use when creating your thermometer? The Celsius scale.

• Was there a difference between the temperature as measured by the “Lab-created thermometer” and the “Reference thermometer?” Student answers may vary depending upon their “Lab-created thermometer.” It is likely that there may be some small differences in the temperatures measured.

• How would you describe the accuracy of the thermometer that you created? Student answers will vary. It is likely that they will describe the “Lab-created thermometer” as less accurate than the “Reference thermometer.”

• Why may there be differences in the accuracy between the “Lab-created thermometer” and the “Reference thermometer?” Students should suggest that the effect of pressure on the boiling point of water may have affected the accuracy of the thermometer. If the students’ location was at an altitude other than sea level (760 mm Hg), the boiling point would not be 100 º C, but rather a lower number. However, according to the procedure, the students would have labeled the mark they made when the thermometer was in the boiling water as 100 º C. This would result in a “Lab-created thermometer” that had its highest reference line a few millimeters lower than the 100 º C line on the “Reference thermometer.” If the “Lab-created thermometer” was made when there was a change in barometric pressure, the boiling point may have also been something other than 100 º C. However, according to the procedure, the students would have labeled the mark they made when the thermometer was in boiling water as 100 º C. This would result in a “Lab-created thermometer” that had its highest reference line a few millimeters different from the 100 º C line on the “Reference thermometer.” Students may also suggest that the “Reference thermometer” had more graduations and thus smaller degree increments than the “Lab-created thermometer.” As a result, the “Reference thermometer” could read the temperature within one degree C. The “Lab-created thermometer” could only read the temperature within ten degrees C with accuracy.

Discuss questions that follow Trial 4.

• Recall Trials 1 and 2. What is the relationship between the kinetic energy of the molecules of liquid inside the “Lab-created thermometer” and the height of the liquid in the thermometer? The greater the kinetic energy of the molecules of liquid inside the “Lab-created thermometer” the higher the level of the liquid in the thermometer. The lower the kinetic energy of the molecules of liquid inside the “Lab-created thermometer” the lower the level of the liquid inside the thermometer.

• What type of physical changes in matter occurs when the kinetic energy of molecules changes? Changes in the kinetic energy of liquid molecules can result in the expansion or contraction of the liquid. As the kinetic energy of the molecules of liquid increased inside the “Lab-created thermometer”, the liquid expanded. As the kinetic energy of the molecules of liquid decreased inside the “Lab-created thermometer”, the liquid contracted. Students may also suggest that changes in the kinetic energy of molecules can result in changes in the phase or state of matter. This is partially correct. Solid, liquid, and gaseous forms of matter differ in the kinetic energy of their molecules. However, to move from one phase to another, the forces or bonds between molecules must ALSO be changed.

• How did the “Lab created and Reference thermometers” measure changes in the kinetic energy of molecules? Both thermometers were constructed with a liquid sealed inside a glass tube. The liquid inside the tube contracted or expanded as the kinetic energy of the molecules of the liquid changed. When thermometers are placed in solids, liquids, or gases, heat is transferred from the areas of higher heat to lower heat. If the heat and the kinetic energy of the molecules of the environment are different from the heat and kinetic energy of the liquid inside the thermometer, there will be a transfer of kinetic energy. As kinetic energy is transferred the liquid inside the thermometer will expand or contract and the level of the liquid will rise or drop inside the thermometer. This raising or lowering of the level of the liquid is associated with a specific scale on the thermometer. The change in the level is therefore given a numerical value that denotes the temperature.

• Look at Table A (above). How did the kinetic energy of the molecules of liquid inside the “Lab created” and “Reference” thermometers change when placed in the three different temperatures of water? Student answers will vary depending upon the temperature read by the thermometer prior to insertion into the three different temperatures of water. Students should indicate that if the level of the liquid in the thermometer dropped once the thermometer was added to the water then kinetic energy was transferred from the liquid inside the thermometer to the liquid in the beaker. If the level of the liquid in the thermometer rose once the thermometer was added to the beaker of water, students should indicate that kinetic energy was transferred from the water in the beaker to the liquid in the thermometer.

• Look at Table A (above). Describe the direction of heat transfer between either of the thermometers and the beaker filled with three different temperatures of water. Student answers will vary depending upon the temperature read by the thermometer prior to insertion into the three different temperatures of water. Students should indicate that if the level of the liquid in the thermometer dropped once the thermometer was added to the water then the heat was transferred from the liquid inside the thermometer to the liquid in the beaker. If the level of the liquid in the thermometer rose once the thermometer was added to the beaker of water, students should indicate that heat was transferred from the water in the beaker to the liquid in the thermometer.

APPLY IT

In Trials 1-4, you observed physical changes in liquids that occurred with the transfer of heat and changes in the kinetic energy of molecules. One of the changes you observed was the expansion of the liquid inside the thermometer as it was heated and the contraction of the liquid inside the thermometer as it was cooled. Look at the pictures below and answer the questions that follow.

• What happened to the kinetic energy of the air molecules as the flask was heated? The kinetic energy of the air molecules increased as the flask was heated.

• Why did the balloon inflate when the flask was heated and deflate when the flask cooled? Use the terms kinetic energy, expansion, and contraction in your answer. As the flask was heated, the kinetic energy of the air molecules inside the flask increased. When this occurred, the air molecules moved faster and farther apart with each vibration. As a result, the air (gas) inside the flask expanded, inflating the balloon. As the flask cooled, the heat was transferred from the air inside the flask and the balloon to the surrounding air. As this happened, the kinetic energy of the air molecules decreased. The decrease in kinetic energy resulted in molecules that moved more slowly and in a decrease in the distance that the molecules moved with each vibration. The air (gas) inside the flask contracted and the balloon deflated.

In Trials 1-4, you observed physical changes in liquids that occurred with the transfer of heat and changes in the kinetic energy of molecules. One of the changes you observed was the expansion of the liquid inside the thermometer as it was heated and the contraction of the liquid inside the thermometer as it was cooled. Look at the pictures below and answer the questions that follow.

• What happened to the kinetic energy of the molecules in the metal ring when the ring was placed in the flame? When the ring was placed in the flame, the heat was transferred to the metal ring. As the heat was transferred to the metal ring, the kinetic energy of the molecules of the metal ring increased.

• What happened to the kinetic energy of the molecules in the metal ball when it was placed in the ice bath? When the metal ball was placed in the ice bath, the heat was transferred from the metal ball to the ice bath. As this happened, the kinetic energy of the molecules of the metal ball decreased.

• Why could the ring fit over the ball when either the ring was placed in the flame or the ball was placed in the ice bath? Use the terms kinetic energy, expansion, and contraction in your answer. When the ring was placed in the flame, the heat was transferred to the metal ring. As the heat was transferred to the metal ring, the kinetic energy of the molecules of the metal ring increased. The molecules moved more quickly and farther apart with each vibration. As a result, the metal ring expanded. The expansion allowed the metal ring to fit over the metal ball. When the metal ball was placed in the ice bath, the heat was transferred from the metal ball to the ice bath. As this happened, the kinetic energy of the molecules of the metal ball decreased. The decrease in kinetic energy resulted in molecules that moved more slowly and in a decrease in the distance that the molecules moved with each vibration. As a result, the metal ball contracted. The contraction of the metal ball allowed it to fit inside the metal ring.

• What conclusions can you make about heat and expansion and contraction of most solids, liquids, and gases? As solids, liquids, and gases are heated, they expand. As solids, liquids, and gases cool, they contract.

• Do you think there may be exceptions to the conclusion you described? Student answers may vary.

• What type of energy changes occurs when matter changes state or phases? Both kinetic and potential energy changes are involved when matter changes phases.