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How To Demonstrate an Endothermic Change – Part 1

How To Demonstrate an Endothermic Change – Part 1

In this short video, Stacey Wheeler will show how to demonstrate an endothermic reaction, which is a concept often covered as part of the GCSE Chemistry topic on energy changes during chemical reactions.

An endothermic reaction is described as a reaction that takes in energy from the surroundings, resulting in a decrease in temperature. This means that the reactants have lower energy than the products.

You will need:

      • 2 x 100cm3 beaker
      • 250ml beaker
      • Small piece of wood to fit the 250cm3 beaker on
      • Thermometer, reading to –30 °C (note 3)
      • Top-pan balance
      • Spatula
      • Water (small amount)
      • Fume cupboard (optional)- this demonstration produces ammonia gas so work in a well ventilated room where possible
      • Barium hydroxide-8-water (CORROSIVE), 32 g
      • Ammonium chloride (HARMFUL), 10 g


  1. Stand the 250cm3 beaker on the block of wood
  2. Add a few drops of water to the wood so that the base of the beaker is touching the water.
  3. Weigh out each chemical into a separate 100cm3 beaker
  4. Mix the two solids in the 250cm3 beaker and stir with the thermometer. The mixture will slowly turn slushy and then a liquid is formed, together with a white suspension.
  5. The presence of ammonia can be detected by smell produced
  6. Observe the drop in temperature, which is confirmed by the fact that the beaker freezes to the piece of wood.
  7. When you have finished observing, drop the whole demonstration into a bowl of water. This will stop anymore ammonia gas being produced

All health and safety measures are the responsibility of the teacher doing the demonstration. It is suggested that you practice before demonstration in front of a class.

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