11-13 yrs old
14-18 yrs old
For chemical reactions to occur the reacting molecules (the reactants) must collide with one another.
March 9, 2020
Temperature and the Rate of a Chemical Reaction
Chemiluminescence of luminol – a cold light experiment
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This lesson is a practical real world experiment. However students can start by constructing glow sticks in Minecraft to introduce the idea that some chemical reactions give off light.
For chemical reactions to occur the reacting molecules (the reactants) must collide with one another. The faster and harder these collisions occur the more rapidly the chemical reaction takes place.
Glow sticks are a good example of a chemical reaction that gives off light. So the amount of light is a good indication of how fast the reaction is happening. The colder the stick the dimmer it will glow and the longer it will last. Conversely warm sticks will glow brighter, but run out quicker.
The basic reactants in glow sticks are hydrogen peroxide and diphenyl oxalate (see resources below). Bending the glow stick breaks a glass tube which releases the hydrogen peroxide allowing it to come into contact with the diphenyl oxalate. The product of the reaction is unstable, and as it breaks down it releases energy which is absorbed by a dye. The energy causes the dye to give off light.
In Minecraft the glow sticks are constructed with luminol which works in a similar fashion.
1) Give each student a bottle.
2) Provide students with access to ice cold and warm water (maximum 50oC)
2) Ask students to mix hot and cold water and fill their bottle with it.
3) Have students measure and record the temperature of the water in their bottles. Write the temperature on the side of the bottle. NOTE: You need to have as wide a range of temperatures as possible. To ensure this is the case you may wish to adjust temperature of a few bottles.
4) Provide students with glow sticks. Make sure they have NOT started them and have the students place the sticks in their bottles. Leave the sticks for 5 minutes.
5) Whilst the sticks are in the bottles ask the students how they will know how fast the reaction in the glow stick is happening. Ask the students to predict what will happen in the cold bottles and what will happen in the warm bottles.
6) Remove the sticks from the bottles, bend them and give them a shake to initiate the chemical reaction. Place the sticks back in the bottle.
7) Line up the bottles and then ask the students to order them from dimmest to brightest.
8) Ask the students what they notice about the temperature of the bottles in the line.
Some glow sticks can be placed in a freezer overnight, whilst others are left out in the warm. Students can put them both in warm water in the morning and then compare how bright they are. The stick kept in the freezer should be brighter as the cold of the freezer will have almost stopped the chemical reaction, so the reactants will have been preserved.
Students should notice that at the end of the experiment the bottles have been lined up in temperature order. This is because the colder glow sticks are reacting slower and so giving off less light.
Students may also notice that the warmer sticks run out quicker. This is because the reactants are used up quicker. This can also be demonstrated by comparing the sticks that have been stored in the freezer overnight, with those left in the open.