Rate of Reaction - Chemistry & Physics

One of the things that students study in Chemistry is the rate of reaction; how fast it goes and what are the factors that control the rate of these reactions. An example from everyday life might be— if you put an iron pipe out in your lawn, how long will it take for it to rust and what factors influence this rusting; like temperature, water, acidity of the water, etc. We often do kinetics studies by observing color changes over time. However, one of the demos I do at the end of the year is the chemiluminescence of luminol (a compound closely related to the materials in light sticks). Luminol produces light when reacting with a strong oxidizer such as ndhydrogen peroxide. After reflecting on this, I thought it might be fun to design an experiment around the rate of this reaction as affected by temperature and concentration.

Integrating a little Physics into the lab (and therefore making interdisciplinary), we used light sensors from the physics lab to measure the intensity of the light in terms of luminous flux. We connected these sensors to a laptop through a software called Sparkvue and we were able to plot out the exponential decay of the intensity of light over time as the reaction proceeded. The graphs produced allowed us to determine the half-life of the reaction and we were able to show direct correlation between rate, concentration and temperature. And if that was not enough, the reaction glows in the dark, which for most of us is just cool and lot of fun.

Michael Rea
HS Chemistry & Physics