9-12

I5: Explain the relationship between temperature, heat, and molecular motion.

Curriculum Organizing Questions	What is the difference between heat and temperature? How does the temperature and molecular motion of this system change as you add/subtract heat?
Elaboration	Heat energy in a material consists of the disordered motions of its atoms or molecules. In any interactions of atoms or molecules, the statistical odds are that they will end up with less order than they began--that is, with the heat energy spread out more evenly. With huge numbers of atoms and molecules, the greater disorder is almost certain. Benchmarks 4E2.
Specific Ideas	Heat consists of random motion and the vibrations of atoms, molecules, and ions. The higher the temperature, the greater the atomic or molecular motion. NSES B5c. The rate of reactions among atoms and molecules depends on how often they encounter one another, which is affected by the concentration, pressure, and temperature of the reacting materials. Benchmarks 4D8.
Developmental & Instructional Implications	Many students' conceptions of heat today are not very different from those of Lavoisier. …Children think of heat as a type of subtle substance, like air, that is capable of flowing into and out of objects. [It] is often thought to have fluid characteristics. Driver p. 138 Generally, pupils [in a study of 13-17 year olds] held the view that heat makes particles move further apart. They appeared to use the underlying model that the volume of a substance increases as its temperature rises, when unfortunately this model does not apply to melting ice. ... Pupils' ideas of the freezing process were expressed in terms of particles becoming more packed together. Driver pg. 94
Examples

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