In the Classroom

Students will learn about energy transformation into a light form (luminescence) and the Bohr model (electron energy levels). This experiment is best fit for students in middle school, high school or college. Students should have an understanding of concepts such as energy transfer between a reaction and the environment, how energy can be measured in the form of light or heat, how temperature can affect the movement of atoms, and brief knowledge of electrons.

 

Science Discipline(s)

Chemistry, Physical Science

 

Topics

Luminescence, Chemical bonds, Chemical reactions, Light, the Bohr model, and electron energy.

 

Activity Title

The effect of temperature on glow sticks

 

Materials

  • 3 beakers
  • 3 identical glow sticks
  • Thermometer
  • Water (hot, room temp, and cold)

 

Procedure

  1. Label beakers A, B, C or hot, cold, room temp.
  2. Fill 1 beaker with hot water, 1 beaker with cold, and 1 with room temperature water.
  3. Break the glow sticks at the same time, shake to mix, then place 1 in each beaker.
  4. Observe how quickly each stick reaches its maximum brightness.

 

Questions

  1. Why does the glow stick not glow before we crack the middle?
  2. How do you know a chemical reaction took place inside the glow sticks?
  3. What does it mean when an electron is “excited”?
  4. What is happening to the atoms inside the glow sticks?
  5. Which beaker went fastest and why? Which beaker went slowest and why?
  6. If you wanted to save your glow stick and make it last longer, what would you need to do to it?

 

Explanation

Did you notice how the glow stick had a light or faint color before you cracked it but then it glowed brightly afterwards? That is because a chemical reaction took place when you broke the middle chamber of the glow stick. When a chemical reaction takes place, energy is released or consumed by the reaction due to the changing of bond. We can measure energy in different ways, emission of light being one of them.

One way to understand why light is being emitted is by saying energy is being released. When an electron is at its ground state, it isn’t taking or releasing energy. When we “excite” an electron however, we give it energy. When there is no more energy to take in, the electrons go back to their ground state and emit light from the releasing of energy. Think of it like stairs, when we stand at the bottom of the stairs, we don’t have any energy. When we want to go up the stairs, we need to gain energy and move up. When we run out of stairs, we have to go back down them. In the case of molecules, they can either “go down the stairs” gradually releasing heat to the environment, or they can “jump” all the way down the stairs releasing energy as light.

From the understanding of why something glows, we turn to what the temperature is doing to the glow stick. When you heat something up, the atoms that make up the mixture start moving really fast and release a whole lot of energy; kind of like how you get hot and tired when you run around. When you cool something off it’s the opposite; the atoms stop moving and save up their energy; just like how we curl up in ball under blankets when were cold. So when we add the glow sticks to the hot water, the atoms start moving around and give off all of their energy. This would make the glow sticks much brighter because the atoms have more energy to give off. When we place the glow sticks in cold water, the atoms move very slowly and save their energy until the heat up. This makes them less bright and last a lot longer than heated glow sticks.

For further understanding or ideas, check out these links below!

http://coolcosmos.ipac.caltech.edu/system/media_files/binaries/68/original/Temperature_and_Glow_Sticks.pdf?1375754120

http://www.acs.org/content/acs/en/education/students/highschool/chemistryclubs/activities/lightsticks-and-luminescence.html