Lesson Plan: Modeling the Melting of Ice FOR THE TEACHER Background Information for Teachers This lesson is rooted in the scientific modeling process. To learn more about modeling in chemistry, read this brief primer or view this screencast. The second half of the lesson makes use of a system of bar graphs for having more quantitative discussions about energy with students. For an introduction into how to use these types of bar graphs, view this screencast.
Submitted by ACS High School Professional Development Team Washington, D.C.
Particulate-level modeling involves representing and describing the arrangement, behavior and interaction of the particles. Macroscopically, we perceive changes in matter as being associated with exchanges of energy. Here we seek to understand how this immaterial concept manifests itself at the particulate level. Much like macroscopic objects, the motion and speed of particles is associated with the kinetic energy of particles. The increase in the average kinetic energy of particles is felt as an increase in the temperature of a system at the macroscopic level. Substances transfer kinetic energy between each other through particle collisions. This transfer of kinetic energy (and resulting temperature changes) is known as heat. In order for thermal energy to be transferred from one thing to another the particles must collide. The specific heat of the substances determine how much energy is needed in the collision to change the kinetic energy (measured macroscopically as temperature) of the particles. The rate of the transfer depends on the thermal conductivity. If the particles are close together they will transfer energy more efficiently. If the particles are large, it may take more energy to increase their kinetic energy. The energy changes that we observe when a substance undergoes a phase change can be explained by using the particulate model of matter. According to this model, phase changes involve the spatial rearrangement of particles (e.g., atoms, molecules) that make up a system. As particles move close to or away from each other, their kinetic and potential energy change. For example, particles that attract each other speed up and gain kinetic energy as they move closer to one another, but their potential energy decreases during the process. Thus, when particles rearrange going from a state in which they are far apart (e.g., gas phase) to a state in which they are closer together (e.g, liquid phase), their kinetic energy increases. As a result, the temperature of the system goes up. Potential energy on the particulate level cannot simply be tied to the relative spacing of particles. The relative arrangement and orientation of particles also affect the interparticle forces that attract particles to each other. Student Prerequisite Information Particulate model of matter, including the behavior of particles in the solid, liquid and gas states of matter as well as the relationship between temperature and average kinetic energy of particles in the system. Resources are provided in Teacher’s Guide for this lesson to help you build this prerequisite knowledge in your students. This activity is intended to be a continuation of the experiences in this lesson on Modeling Energy Transfer.
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Additional Resources: To learn more about energy in physical and chemical changes: • ACS. Energy Foundations for High School Chemistry. http://highschoolenergy.acs.org/content/hsef/en.html • ACS. Exothermic, endothermic, & chemical change. http://highschoolenergy.acs.org/content/hsef/en/how-can-energy-change/exothermicendothermic-chemical-change.html • To learn more about the chemistry of reusable hand warmers: • http://home.howstuffworks.com/question290.htm • http://www.heatinasnap.net/FAQ.html#22 • To learn more about students’ misconceptions about energy in physical and chemical processes: • http://www.rsc.org/images/Misconceptions_update_tcm18-188603.pdf • http://pubs.acs.org/doi/abs/10.1021/ed081p523 • http://pubs.acs.org/doi/abs/10.1021/ed069p191?journalCode=jceda8 • http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3671656/ To learn more about facilitating small and large group discussions: • http://inquiryproject.terc.edu/shared/pd/TalkScience_Primer.pdf • https://www.nsta.org/store/product_detail.aspx?id=10.2505/9780873537452 To learn more about how to build an understanding of the particulate-level behavior of particles in a solid, liquid and gas: • https://www.gvsu.edu/targetinquiry/tidocuments-home.htm (register for the site and find the “Putting the World in a Box” activity) • http://modelinginstruction.org/teachers/resources/chemistry-core-units/ There are a variety of interactive computer simulations that illustrate how the particulate and molecular models of matter can be used to explain physical and chemical changes: • http://phet.colorado.edu/en/simulation/gas-properties • http://phet.colorado.edu/en/simulation/states-of-matter • http://phet.colorado.edu/en/simulation/states-of-matter-basics • http://www.cbc.arizona.edu/tpp/chemthink/resources/U1_M2/partmodel4.html • http://mw.concord.org/modeler/ (Click on “Showcase” at the top menu on this page, and then “Click” “Chemistry” on the next page to display chemical models. These models illustrate a variety of physical and chemical processes). • http://lab.concord.org/embeddable.html#interactives/sam/phase-change/6-phase-changescaused-by-energy-input.json • http://lab.concord.org/embeddable.html#interactives/student/stateofmatter/latentheat2.json • http://lab.concord.org/embeddable.html#interactives/student/stateofmatter/latentheat3.json
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