Module: Changes in Energy on the Molecular Level
DCI: PS1.A (C) Gases and liquids are made of molecules or inert
atoms that are moving about relative to each other.
DCI: PSI.A (D) In a liquid, the molecules are constantly in contact
with other; in a gas, they are widely spaced except when they happen to
collide. In a solid, atoms are closely
spaced and may vibrate in a position but do not change
relative locations.
DCI: PS1.A (F) The changes of state that occur with variations in
temperature of pressure can be described and predicted using these models of
matter.
PE: MS-PS1 -4 Develop a model that predicts and describes changes
in particle motion, temperature, and state of a pure substance when thermal
energy is added or removed.
[Clarification
Statement: Emphasis is on qualitative molecular-level models of solids,
liquids, and gases to show that adding or removing thermal energy increases or
decreases kinetic energy of the particles until a change of state occurs.
Examples of models could include drawing and diagrams. Examples of particles
could include molecules or inert atoms. Examples of pure substances could
include water, carbon dioxide, and helium.]
It may be tempting to ask questions about the arrangement of molecules in a solid, liquid, or gas. While these types of questions seem to be perfectly within the standard, they may in fact, be too low level for middle school.
A better approach will be to ask about the changes in the particle motion when energy is added or removed. It is safe to use both particles and pure substances (listed above) in questions.
A better approach will be to ask about the changes in the particle motion when energy is added or removed. It is safe to use both particles and pure substances (listed above) in questions.
Possible Question Starters:
"Which of the following changes would result in an increase in the motion of particles in a substance?"
correct answer = adding heat energy to the substance
wrong answer = moving the substance to a different container
Conversely...
"As a substance loses heat energy, which of the following changes is most likely to its atoms?"
correct answer = distances between atoms will decrease
wrong answers = DON'T say "distances increase" or "distances stay the same"! Maybe "atoms will increase in speed", or other characteristics that will clearly not change.
Conversely...
"As a substance loses heat energy, which of the following changes is most likely to its atoms?"
correct answer = distances between atoms will decrease
wrong answers = DON'T say "distances increase" or "distances stay the same"! Maybe "atoms will increase in speed", or other characteristics that will clearly not change.
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