Extreme+Phase+Changes

=Extreme Phase Changes=

Author: Dorothy Ahlf, 2011

Purpose: To show the students some of the more extreme examples of solids and liquids, and how they can be useful in research. For the students to start to think about safety in handling substances and to think about where cryogens could be useful.

Overview: Students will already have prior knowledge of phase changes and some substances, so the lesson will focus on the more “extreme” ones used in research at Northwestern University or other areas. We will discuss these substances in general, with real examples in front of the students (liquid nitrogen, dry ice) so we will talk them through why they are used and think about some of the advantages and disadvantages for using them. At the end for fun and a special treat, we will make liquid nitrogen ice cream!

Student Outcomes: Students should be able to remember several concepts covered before like phase changes, sublimation, and conversion of temperatures between Fahrenheit, Celsius, and Kelvin. Students should be able to describe some of the physical characteristics associated with cryogens. Students should be able to reason through some of the hazards when handling substances like cryogens and design a way to mitigate some of the hazards for use.

Possible Standards Impacted: 12.C.3a Explain interactions of energy with matter including changes of state and conservation of mass and energy. 12.C.3b Model and describe the chemical and physical characteristics of matter (e.g., atoms, molecules, elements, compounds, mixtures). 13.A.3a Identify and reduce potential hazards in science activities (e.g., ventilation, handling chemicals) 13.B.3a Identify and explain ways that scientific knowledge and economics drive technological development. 13.B.3c Describe how occupations use scientific and technological knowledge and skills.

Teaching Notes: 1) Review Phase changes and what they know about them for about 5 minutes. See if they can draw a phase diagram on the board/tell me about the one I have up (label parts that are solid, liquid, and gas). 2) As them about the part of the diagram that contains the transition between vapor to solid. 3) Show dry ice for those who haven’t seen it. Discuss what this is used for or could be used for. 4) Ask them about ways they could make things even colder. 5) Introduce Cryogens-safety ideas, containing, transporting, etc (see worksheet) 6) Pictures/Videos of where Cryogens are used at Northwestern in the KRG 7) Ice Cream! 8) If time: brainstorm more places cryogens could be used or see what they’ve retained (Math between Fahrenheit, Celsius, Kelvin?)

Assessment: I’ve made a short worksheet for the students to take notes/write thoughts on, but most of the assessment will be done by in-class question and answer sessions while the demonstrations are going on.

Handout: [|Extreme Phases.docx]