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K–12 teaching and learning · from the UNC School of Education

Physical and chemical changes

This is a PowerPoint presentation to help students distinguish between physical and chemical changes. It includes teacher demonstrations to check the students' understanding.

A lesson plan for grade 8 Science

By Louise Whealton

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Learning outcomes

Students learn to distinguish between physical and chemical changes by comparing their observations to a list of clues to recognizing types of change.

Teacher planning

Time required for lesson

45 minutes

Materials/resources

  • scrap paper
  • matches
  • beaker
  • water
  • salt
  • spoon
  • hot plate or Bunsen burner
  • flask or soda bottle
  • balloon
  • vinegar
  • baking soda
  • funnel

Technology resources

Pre-activities

This presentation can be used as an introduction to chemical and physical changes. Students can be successful at it with no prior knowledge. It can also be used after studying the properties of chemicals.

Activities

The teacher should set up the computer display so that it is visible to the entire class. Load and view the PowerPoint presentation. Students take notes from the first eight slides of the presentation.

Beginning with the ninth slide, the teacher clicks the mouse once to cause the question to appear. Perform the demonstration that is mentioned on the slide. Ask the students to decide whether the demonstration illustrated a physical or chemical change. They should refer to the notes they just copied and be able to explain why they decided on their answer. When the class has reached consensus, click the mouse to cause the answer to appear on the screen. The demonstrations are:

  1. Tear up a piece of paper.
  2. Dissolve a spoon of salt in a beaker of water.
  3. Burn a small piece of torn up paper.
  4. Pour a small amount of the salt water into another beaker and heat it until the water evaporates and leaves the salt. Note: you may want to start this demonstration before you burn the paper. That way the water will be evaporated about the time you want to discuss it.
  5. Place some vinegar in a flask or coke bottle. Use the funnel to put some baking soda into the balloon. Fasten the balloon over the mouth of the flask. Lift the balloon up so that the baking soda falls down into the vinegar.

Assessment

Make up some real life examples of changes and ask the students to decide if they are chemical or physical changes. Some examples I have used are:

  • cutting grass
  • burning toast
  • making tea with a tea bag and water
  • wadding up your homework and throwing it across the room
  • ice cream melting
  • frying an egg
  • gasoline combustion in a car
  • sweat evaporating from your forehead

I have also asked students to list examples they notice themselves.

Supplemental information

Comments

I use this to introduce physical/chemical changes. I follow it with several labs the students do themselves. Each of these labs refers back to this presentation.

If you have your own favorite demonstrations, you can edit the PowerPoint presentation to include them.

North Carolina Curriculum Alignment

Science (2005)

Grade 8

  • Goal 4: The learner will conduct investigations and utilize technology and information systems to build an understanding of chemistry.
    • Objective 4.01: Understand that both naturally occurring and synthetic substances are chemicals.
    • Objective 4.02: Evaluate evidence that elements combine in a multitude of ways to produce compounds that account for all living and nonliving substances.
    • Objective 4.03: Explain how the periodic table is a model for:
      • Classifying elements.
      • Identifying the properties of elements.
    • Objective 4.06: Describe and measure quantities related to chemical/physical changes within a system:
      • Temperature.
      • Volume.
      • Mass.
      • Precipitate.
      • Gas production.
    • Objective 4.07: Identify evidence supporting the law of conservation of matter.
      • During an ordinary chemical reaction matter cannot be created or destroyed.
      • In a chemical reaction, the total mass of the reactants equals the total mass of the products.