Physical and Chemical Changes

By: Doris Hoyos and Priya Vanparia

Introduction

Have you ever wondered why fireworks "boom" after they are shot in the sky? Or why your ice cream drips in the summer heat? These occurrences are caused by chemical and physical changes. In this unit we will discuss what these changes are, and how we can identify them.

Physical Change

Physical Change is an alteration that only changes the appearance of a substance, and not the actual substance itself. During this process, compounds are rearranged but are not changed internally. Most physical changes alter the size and shape of a substance, and are reversible.

Chemical Change

Chemical Change is an alteration that produces a new substance. During this process reactants change into new products, and compounds are either formed or broken. Most chemical changes are irreversible.

Indications of Chemical Change

  • Change in color, smell, or temperature
  • Production of energy in light, sound, movement or and gas form.
  • Formation of a precipitate (solid particles separated from the solution)

Questions

  1. What happens to compounds during a chemical change?
  2. Is a snowman melting a physical or chemical change?
  3. True or False: Change in size or shape is an indication of chemical change.
  4. Is the baking of a cake a chemical or physical change?
  5. True or False: A physical change is reversible.