Background: In chemical reactions, energy can be given off or absorbed in the form of heat but it can also be given off or absorbed in the form of light. Glow sticks use a chemical reaction between a substance called luminol and hydrogen peroxide to release energy in the form of light. How do you start a glow stick? Yes you bend the stick, which breaks a small container filled with a chemical inside the light stick. Once broken, the chemicals which were separate combine and react with each other. When you are not using a glow stick you keep it in the freezer and it lasts longer. Why is this? Surely temperature has something to do with the rate of the chemical reaction. At the end of this short experiment you will know why

  • A cup/beaker of hot water
  • A cup/beaker of ice cold water
  • 2 glow sticks

 

1. If in packaging, remove the glow sticks from the packet. DO NOT BEND
2. Place 1 glow stick in the ice cold water and place the other glow stick in the hot water
3. Leave the glow sticks in the water for 5-7 minutes
4. After this time remove the glow sticks from both the hot and cold water
5. Bend the glow sticks to start them off, you should hear a popping noise.
6. What do you observe? Is there a difference between the hot and cold glow stick?
Discussion:So, why does this happen? When the reactants are heated, the average kinetic energy of the molecules increases. This means that more molecules are moving faster and hitting each other with more energy. Molecules need to hit each other with enough energy in order to react. If more molecules hit each other with enough energy to react, then the rate of the reaction increases.
Extension: Take the cold glow stick that was in the icy water and heat it up by rubbing it between your palms, the friction and heat speeds up the reaction causing the glow stick to give of light again. Alternatively you could place the glow stick in a beaker of hot water.

What did you discover?

Tweet or email pictures of your bright and dull glow sticks to:
#chemistry4all #LJMU_CfA #CfALavaLamp  chemistryforall@ljmu.ac.uk

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