Skip to content
Grades 7 and 8 Intermediate About 15 min Version 1 Awaiting review Premium

Signs of a chemical reaction

In a chemical reaction, substances change into new substances. We cannot see the particles rearranging, but we can look for evidence: bubbles of a gas, a new solid appearing in a liquid, a colour change, or a change in temperature. When a substance only dissolves or changes shape, no new substance forms. That is a physical change.

What you will learn

  • List observable evidence that a chemical reaction has happened.
  • Identify gas production and the formation of a new solid as evidence of a reaction.
  • Tell a chemical change apart from dissolving, which is a physical change.

Before you start

  • Know that dissolving does not make a new substance. Try the Dissolving experiment first.

Materials

  • Vinegar
  • Baking soda
  • Milk
  • Water
  • Table salt

Equipment

  • 3 beakers (100 mL)
  • Stirring rod

Procedure

  1. Pour 20 mL of vinegar into Beaker A, then add 5 g of baking soda.
  2. Pour 20 mL of milk into Beaker B, add 20 mL of vinegar and stir.
  3. Pour 20 mL of water into Beaker C, add 5 g of salt and stir.
  4. Record the evidence you see in each beaker, or the lack of it.

How this simulation is simplified

  • The bubbling is shown continuing. In real life it slows down and stops once the baking soda or the acid in the vinegar is used up.
  • Changes in temperature are not shown here, although they can also be evidence of a reaction.