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.


  • Mathematics > General

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