![]() Will you need to put a drop of water on just one paper towel or on two? As you listen to students, help them realize that they will need to wet two paper towel samples but that only one will be heated. Tell students that they will test the evaporation of just 1 drop of water on a brown paper towel so that they can see results quickly.Īsk students: What could you do to make a small amount of water evaporate faster from a paper towel? Students will know that they should somehow heat the water on the paper towel. Help students design an experiment to find out whether adding energy increases the rate of evaporation.Tell students that they are going to find out what happens to water molecules as they evaporate by exploring how to make water evaporate faster. The water molecules separate and are in the air as a gas called water vapor. When water evaporates, where do the water molecules go? Make it clear that, although you can’t see the water anymore after it has dried up or evaporated, it still exists. What are some other examples of evaporation? Students may think of common examples of evaporation such as clothes in a dryer, wet hair drying on its own, or a puddle drying up in the sun. Point out that the word “evaporate” has the word “vapor” in it-water changes to water vapor but it is still water. Explain to students that when water evaporates, it changes from a liquid to a gas. They may say that the water will evaporate. Place both paper towels up in a prominent location.Īsk students: At the end of class, do you think the paper towel will still be wet or will it be dry? Students should agree that the wet paper towel will likely become dry. Select a student to feel the difference between the two paper towels now, and again at the end of the class period. Dampen one with water so that the color appears darker than the dry piece of paper towel. Show students two pieces of brown paper towel. Engage Predict what might happen to a wet paper towel by the end of the class. ![]() Note: Energy can also be transferred through radiation and convection, but this chapter only deals with heat transfer through conduction. 2 quart-size zip-closing plastic storage bags.Make sure you and your students wear properly fitting goggles. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. Evaluationĭownload the student activity sheet, and distribute one per student when specified in the activity. Students will be able to explain, on the molecular level, why adding energy increases the rate of evaporation. Students will be able to identify and control variables to design a test to see if heating water affects the rate of evaporation. Students will create 3-D Styrofoam models of water molecules. Students will be introduced to a more detailed model of the water molecule. Students will look at molecular animations to help explain why the heating water increases the rate of evaporation. Students will help design an experiment to see if adding energy (heating) affects the rate of evaporation. To conduct a valid experiment, variables need to be identified and controlled.Adding energy increases the rate of evaporation.Evaporation occurs when molecules in a liquid gain enough energy that they overcome attractions from other molecules and break away to become a gas.Settlement of these contradictions leads to the conclusion that like PVA's melting point, its glass transition is also a thermochemical transition but with no detectable mass loss. Contradictions among the conclusions from various analytical techniques, regarding the glass transition of PVA, are discussed and interpreted. Activation energy's contribution to the specific heat of thermochemical transition seems to be low. It is shown that the value of specific heat of thermochemical transition is comparable to theoretical values derived from chemical bond dissociation energy values. In this work, differential scanning calorimetry (DSC), isothermal and non-isothermal thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), optical microscopy, viscometry and kinetic modeling were used to study the thermal behavior of PVA for providing further insights about the thermochemical transition. Poly(vinyl alcohol) PVA is a synthetic polymer used in a variety of applications and exhibits unusual thermal behavior.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |