Key Idea: For any single state of matter, the average speed of the atoms or molecules increases as the temperature of a substance increases and decreases as the temperature of a substance decreases.

Students are expected to know that:

  1. The temperature of a substance is directly related to the average speed of its atoms/molecules.
  2. Therefore, as matter in any particular state is heated, stirred, shaken, etc., the average speed of its atoms/molecules increases, which is reflected in an increase in its temperature.
  3. As matter in any particular state cools, the average speed of its atoms/molecules decreases, which is reflected in a decrease in its temperature.
  4. When the temperature of matter in any particular state remains constant, the average speed of its atoms/molecules remains constant, and when the average speed of the atoms/molecules of matter in any particular state remains constant, the temperature of the matter remains constant.

Boundaries:

  1. Students are not expected to know that temperature remains constant during a change of state, which is a later idea.
  2. They are not expected to know the term kinetic energy or that kinetic energy is a function of mass and velocity.
  3. Students are also not expected to know that atoms and molecules of different substances move at different speeds at the same temperature.
  4. They are not expected to know that increasing pressure will increase the temperature or any other application of the gas law equations.
  5. Students are also not expected to know the special case of absolute zero temperature where, according to kinetic theory, there should be no motion.