Modeling Chemistry Workshop – Day 4 Part 1

We actually ended Day 3 with this dilemma (that you could pose to your students as well) and came back to it at the start of Day 4.

We have the following particle pictures:

show temp press

One of these pictures shows particles at 1 atm and the other at 5 atm. Which is which?

Particles in one picture are at 20 °C in the other picture they are at 50 °C. Which is which?

How can we show pressure and temperature in our particle pictures?

Note: In the discussion that results, you might get a response like this: “The heat would make the particles go faster than the cold.”  At this point it will be helpful to outlaw the use of the word “heat”.  Better to use hot/cold and energy being added or taken away.

Temperature

(notes for students)

Definition: a measure of how fast particles are moving  (our evidence for this definition can be the movement we saw with dyes in the hot and cold water)

Standard Temperature: 0° C

How Do We Measure It: with a thermometer (by thermal expansion) – the transfer of energy from the hotter item changes particle movement resulting in the height of the liquid in the thermometer changing

How Do We Represent It: use “whooshies” (trailer(s) behind a particle to show how fast it is moving/where it is coming from), more whooshies = higher temperature, whooshies are qualitative representations  (there isn’t a set number or whooshies for each temperature)

(In our workshop we discussed letting students come up with ideas on how to represent various temperatures and steering them towards whooshies.)

whooshies

Pressure

(notes for students)

Definition: particle collisions with the container

Standard Pressure: 1 atm, 760 mmHg, 100 kPa

How Do We Measure It: with a pressure gauge/manometer, the collisions push on the gauge or liquid; pressure sensor (apparently Vernier has a great explanation in their pamphlet, but I haven’t checked into it yet.)

How Do We Represent It: an “x” marking the “pressure event” on the wall where the particle must have hit (see picture below), think of this as tracing the whooshie backwards to see where the collision must have taken place

press events

To complete the KMT info that students need tell students:

Particles move in straight lines.

Particles don’t slow down or stick to each other when colliding.

Student Panel

Even though this happened last during Day 4, it makes most sense to tack this on here, since the next chunk of Unit 2 material is rather substantial.

We heard from a panel of students that have taken modeling courses to find out their views and then also discussed what we heard.  Here are the most interesting tidbits I took away (as I’m writing this I realize this doesn’t represent the conversation very well, but these are the things that I felt I’d want to do in my class):

  • Students in many classes use a “statement of despair” when necessary on homework.  In other words, rather than just leaving something blank and saying “I tried but didn’t get it” (like has often happened in my classes), students need to state what it is that is giving them trouble (be specific).  I LOVE this idea and plan to implement it!
  • Students use homework as a first attempt and will write a second attempt at a problem after whiteboarding sessions.  (I think some classes even use homework sheets designed with spaces for 1st and 2nd attempts.)
  • Students liked when there was variety in whiteboarding and working in groups, pairs, and by themselves.
  • Some teachers find it helpful to say they will be grading whiteboards, even if they don’t plan to include them in a grade.
  • If a wrong whiteboard is presented and none of the students challenge it, you might just let it go and give a quiz on it the next day.  This might be one way to emphasize that whiteboard sessions are for students (not you).

Up Next: PVTn Lab

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