What are physical and chemical changes?  

Here is a short video that introduces the difference between the two: Physical/Chemical Changes Video

Example of Chemical Changes Video

If you aren’t able to watch the videos: 

Physical Change: 

  • waking, cooling, cutting, bending, stirring, mixing
  • materials may be combined or physically changed to be used in different ways (for example: plants can be ground up and combined with other materials to make dyes)

Chemical Change: 

  • cooking, burning, etc.
  • materials are combined to form a new substance- a chemical reaction is created which forms the new substance and can’t be reversed or undone

Optional: Try it at home with an adult! Below is a recipe for play dough that I use for the classroom, see if you can identify when you see a physical change and when you see a chemical change! Can you think of some other examples of physical and chemical changes that you can see at home besides baking or cooking? 

Materials:

  • 1 cup of flour
  • 1/4 cup of salt
  • 3/4 cup of water
  • 3 tablespoons of lemon juice
  • 1 tablespoon of vegetable oil
  • Food colouring
  • Any seasonings or scents you would like

Directions:

  • Add the water, oil and lemon juice to a medium non-stick pot and heat on medium heat on the stove (maybe even slightly lower heat depending on your stove).
  • Add food colouring, liquid scents or Kool-aid to the water mixture.
  • In a mixing bowl, combine the flour, salt and any dry seasonings you are using.
  • After the water is hot, but not boiling, slowly add the dry ingredients to the pot and while mixing to combine. I use a wooden or plastic cooking spoon.
  • Continuously stir until the ingredients combine, dry out and begin to form a ball. If there are parts that seem a bit sticky still, just flatten the dough out and put the sticky side down on the bottom of the pot very briefly. Flip back and forth frequently until it doesn’t seem sticky anymore. However, don’t cook it too long. It is better to be a bit undercooked as it will firm up as it cools down.
  • Place on a sheet of wax paper until it cools down a bit. Then knead the dough for a minute or two to bring it all together.