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published by the American Chemical Society
written by Patti Galvan and Jim Kessler
This multimedia lesson by the American Chemical Society explores factors that affect the motion of molecules. Students add food coloring to a cup of ice water and a cup of hot water, then analyze the difference in how the colors spread/diffuse through each cup. Two interactive animations help them visualize what is happening: heating a substance increases molecular motion, while cooling decreases it.

Editor's Note: Often, students in the middle grades have difficulty comprehending why the measured volume increases slightly when water is heated. Many have the misconception that volume is always conserved in a physical change. This resource provides a clear way to understand the volume differences that can occur when molecules move further apart or closer together by heating/cooling.

Included in the lesson is a student activity sheet with answer key and suggested discussion questions.

Please note that this resource requires Flash.
Subjects Levels Resource Types
General Physics
- Properties of Matter
Modern Physics
- Atomic Physics
= Atomic Models
Other Sciences
- Chemistry
Thermo & Stat Mech
- Thermal Properties of Matter
- Middle School
- Informal Education
- Instructional Material
= Curriculum
= Instructor Guide/Manual
= Interactive Simulation
= Lesson/Lesson Plan
= Problem/Problem Set
- Audio/Visual
= Movie/Animation
Intended Users Formats Ratings
- Educators
- Parent/Guardians
- Learners
- Administrators
- General Publics
- text/html
- application/flash
- application/pdf
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Free access
© 2010 American Chemical Society
chemistry animations, chemistry videos, heat and temperature, liquids, molecular structure, properties of liquids, state changes, states of matter, thermal properties, volume, volume of liquids
Record Cloner:
Metadata instance created April 27, 2011 by Caroline Hall
Record Updated:
October 7, 2012 by Caroline Hall
Last Update
when Cataloged:
January 31, 2011
Other Collections:

AAAS Benchmark Alignments (2008 Version)

4. The Physical Setting

4D. The Structure of Matter
  • 6-8: 4D/M1a. All matter is made up of atoms, which are far too small to see directly through a microscope.
  • 6-8: 4D/M3ab. Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated.
  • 6-8: 4D/M3cd. In solids, the atoms or molecules are closely locked in position and can only vibrate. In liquids, they have higher energy, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions.
  • 6-8: 4D/M8. Most substances can exist as a solid, liquid, or gas depending on temperature.
  • 6-8: 4D/M10. A substance has characteristic properties such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it.

11. Common Themes

11B. Models
  • 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.
  • 6-8: 11B/M6. A model can sometimes be used to get ideas about how the thing being modeled actually works, but there is no guarantee that these ideas are correct if they are based on the model alone.
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Record Link
AIP Format
P. Galvan and J. Kessler, (American Chemical Society, Washington DC, 2010), WWW Document, (
P. Galvan and J. Kessler, Middle School Chemistry: Molecules in Motion (American Chemical Society, Washington DC, 2010), <>.
APA Format
Galvan, P., & Kessler, J. (2011, January 31). Middle School Chemistry: Molecules in Motion. Retrieved January 28, 2023, from American Chemical Society:
Chicago Format
Galvan, Patti, and Jim Kessler. Middle School Chemistry: Molecules in Motion. Washington DC: American Chemical Society, January 31, 2011. (accessed 28 January 2023).
MLA Format
Galvan, Patti, and Jim Kessler. Middle School Chemistry: Molecules in Motion. Washington DC: American Chemical Society, 2010. 31 Jan. 2011. 28 Jan. 2023 <>.
BibTeX Export Format
@misc{ Author = "Patti Galvan and Jim Kessler", Title = {Middle School Chemistry: Molecules in Motion}, Publisher = {American Chemical Society}, Volume = {2023}, Number = {28 January 2023}, Month = {January 31, 2011}, Year = {2010} }
Refer Export Format

%A Patti Galvan %A Jim Kessler %T Middle School Chemistry: Molecules in Motion %D January 31, 2011 %I American Chemical Society %C Washington DC %U %O text/html

EndNote Export Format

%0 Electronic Source %A Galvan, Patti %A Kessler, Jim %D January 31, 2011 %T Middle School Chemistry: Molecules in Motion %I American Chemical Society %V 2023 %N 28 January 2023 %8 January 31, 2011 %9 text/html %U

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Middle School Chemistry: Molecules in Motion:

Is Associated With Middle School Chemistry: The Ups and Downs of Thermometers

This lesson would be a good follow-up. It features an experiment and two related animations that allow students to explore why the liquid in a thermometer goes up and down depending upon the amount of heat or cold.

relation by Caroline Hall

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