Lightstick Reaction Rates
Three commercial glow sticks are started. One is immersed in a hot water bath. It glows more brightly. Another is immersed in an ice water bath. It glows more dimly. This illustrates how temperature affects rates of reaction.
This demo is usually performed when factors that affect the rate of reactions are being discussed. Allow about 10 minutes for this demo.
Raising the temperature of a reaction mixture results in both more frequent and more energetic molecular collisions. This increases the rate of reaction. In a chemoluminescent reaction such as this one, the increased reaction rate can be perceived as increased brightness. The chemical reaction in a light stick usually involves several different steps. A typical commercial light stick holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here's the sequence of events when the two solutions are combined:
- The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester.
- The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound.
- The cyclic peroxy compound decomposes to carbon dioxide.
- This decomposition releases energy to the dye.
- The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy in the form of light.
- 3 light sticks with strings tied to them
- a beaker containing hot water
- a beaker containing ice water
- Dim the lights.
- Snap and shake the three light sticks so that they begin to glow.
- Place one of the light sticks in the beaker containing ice water and another in the beaker containing the hot water. The third light stick serves as a control. Leave the light sticks in their respective beakers for about thirty seconds.
- Withdraw the light sticks from their beakers using the attached strings. Compare their relative brightness. The light stick that was immersed in the hot water should be brighter than the control stick and the stick that was immersed in the ice water should be dimmer than the control stick.
- You will be working around very hot water in conditions of impaired visibility (dim light). Be careful, hot water can cause severe burns.
- Vapor pressure can build up in the heated light stick and the heat weakens the plastic. Light sticks have been known to burst under these conditions, so wear goggles to protect your eyes.
You can get light sticks at the Hiron's on Franklin Blvd.