ChemCrafter
Submitted by Michelle Personick, Wesleyan UniversityStudent learning is not assessed directly after the activity, but rather is assessed indirectly through student performance on related homework and exam questions. More specifically, the second section of the exams in my general chemistry course always asks students to "provide a concise (but complete) explanation or rationalization for [some number] of the following statements." This section is particularly suited to assessing the learning goals above.
This activity was recently introduced, and student performance has not been evaluated yet.
ChemCrafter, from the Science History Institute (formerly the Chemical Heritage Foundation), is a free iPad app that mimics a classic chemistry set. It is set up as a game, with three sections: reactions with water, reactions with acid, and salts. The app shows the progress of the reaction (smoke, color change, etc.) when two elements are mixed in a reaction vessel, and also gives the change in enthalpy of the reaction.
Pros: It's a safe and fun way to demonstrate some visually exciting chemical reactions. It's free and the graphics are high quality. The app projects well on a large screen using a standard classroom projector.
Cons: Accessing later sections of reactions requires completion of the previous sections, and there is some artificial gating of chemical and glassware replenishment behind wait times. As a result, it's best used as a demo rather than as a dry lab. It's also only available for the iPad.
Students should be able to explain the difference between thermodynamics and kinetics.
Students should be able to explain why even thermodynamically favorable reactions sometimes do not proceed on an observable timescale.
Students should be able to explain why heat is sometimes necessary to make a highly exothermic reaction proceed.
Once everything is unlocked, it's possible to set up any reaction using the chemicals in the given "set" for each category of reaction. I use ChemCrafter in my second semester general chemistry course to transition from a unit on reactions of ions in aqueous solution (hydration/hydrolysis, Bronsted acid/base and hard-soft acid base principles of solubility/reactivity, etc.) to a unit on kinetics. I show a series of reactions from the salt section that the students would expect to have roughly increasing enthalpies of lattice formation based on the Born-Lande equation:
[Note: All reactants are in their elemental form in the app, so the enthalpies of formation aren't truly lattice energies.]
2 Na + Cl2 --> 2 NaCl (1+ cation with a 1- anion)
2 K + F2 --> 2 KF (1+ cation with a 1- anion)
Zn + Cl2 --> 2 ZnCl2 (2+ cation wtih a 1- anion)
These combinations were selected because their reactions in the app become increasingly dramatic (and colorful) in this order. I then show the students a set of reactions that they would expect to be even more exciting, but which don't actually proceed without heat. They hold their breath for the first one to react.
Zn + S --> ZnS (2+ cation with a 2- anion)
2 Al + 3 I2 --> 2 AlI3 (3+ cation with a 1- anion)
The app provides an option for heating these mixtures of elements with a bunsen burner, and then they react dramatically. At this point, we're ready to discuss the difference between thermodynamics--which is all they've seen up to this point--and kinetics.
