Why do some things get colder (or hotter) when they react? [v1.0]

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SYNOPSIS

In this unit, students start by observing a perplexing phenomena.   When two solids are mixed together in a beaker, the beaker drops in temperature so much, that it freezes to a wooden block it is sitting on!    This leads students to start wondering about whether temperature changes occur when other things are mixed together.  As students investigate other phenomena, they develop models to answer to the question, “Why do some things get colder (or hotter) when they react?


What students figure out:   

By the end of the unit, students develop ideas about the structure and properties of matter, chemical reactions, and the relationship between energy and forces.  These ideas include:  

  • A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
  • When two objects interacting through a field change relative position, the energy stored in the field is changed.
  • Whether or not energy is stored or released in a chemical process, can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy.

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