Many chemical reactions produce both light and heat. A burning candle is such a reaction. When a candle is lit, its flame both glows and becomes hot. It is much less common for a chemical reaction to produce light without heat. The light from such reactions is called cool light, because it is created without heat. Reactions that produce light without heat are called chemiluminescent reactions. Perhaps the most familiar chemiluminescent reactions are those that occur in living organisms. Fireflies produce light without heat by a chemiluminescent reaction. Chemiluminescent reactions that occur in living organisms are called bioluminescent reactions.
In this activity you will examine a commercial chemiluminescent chemical reaction. The reaction occurs inside a Lightstick. Lightsticks are available at many sporting goods stores, camping supply stores, and hardware stores. (Lightsticks are available from Educational Innovations) Amusement parks and carnivals often have them in the shape of bracelets and necklaces.
|Open the wrapper and remove the Lightstick.|
|Describe the Lightstick. What does it look like? What color is it? How big is it? Is anything inside the Lightstick?|
Immediately before activating the Lightstick, record today's date and the time:
|Date: ____________________||Time: ____________________|
Follow the directions on the wrapper to activate the Lightstick:
|Observe the Lightstick in a darkened room.|
|Describe the appearance of the Lightstick. What is the color of the glow? Does the glow come from the entire Lightstick or only from the liquid inside the Lightstick?|
|Immerse the Lightstick in a glass of ice water for five minutes.|
|Does chilling the Lightstick affect its glow? What happens to the glow?|
|Immerse the Lightstick in a glass of warm water for five minutes. DO NOT USE BOILING WATER OR PLACE THE LIGHTSTICK IN THE OVEN. THE PLASTIC SHELL OF THE LIGHTSTICK CAN MELT.|
|What happens to the glow when the Lightstick is warmed?|
Summarize how temperature affects the glow of the Lightstick.
|Put the glowing Lightstick in the freezer for at least 24 hours.|
|Does the Lightstick continue to glow while it is in the freezer?|
|Remove the Lightstick from the freezer and allow it to warm to room temperature.|
|Does the glow come back when the Lightstick returns to room temperature?|
|Observe your Lightstick periodically during the day.|
|How does the glow change with time? How long does it take for the glow to disappear? Where did you keep the Lightstick? What was the approximate temperature of the Lightstick? What could be done to preserve the glow of the Lightstick?|
In this activity you observed the effect of temperature on the glow of a Lightstick. This effect is a result of the effect of temperature on the rate of the chemical reaction that produces the glow. Like all chemical reactions, the reaction that produces the glow is slower at lower temperatures and faster at higher temperatures. In a Lightstick, the faster the reaction the brighter the glow. When the reaction in a Lightstick occurs at a faster rate, it will use up the reactants inside more quickly than when the reaction occurs more slowly. Can you devise an experiment that would test this statement?
|For additional information, see CHEMICAL DEMONSTRATIONS: A Handbook for Teachers of Chemistry, Volume 1, by Bassam Z. Shakhashiri, The University of Wisconsin Press, 2537 Daniels Street, Madison, Wisconsin 53704.|
Fireflies use cool light (nearly 100% efficient!) to communicate with each other and to warn off predators.
Learn more in this Science Friday video