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The rate of reaction is the speed at which reactants are converted to products in a chemical reaction. It is an important topic in chemistry, as the rate of reaction can offer many important insights into the nature of various substances. It is also important in industries that must produce some chemicals on a large scale, as the reactions that produce such chemicals must progress at a high enough rate. Some reactions may occur almost instantaneously while others may take hours, days, or even years to progress to completion. In academics, reaction rates are a subset of the topic of chemical kinetics, which is included under the title of physical chemistry.
There are many different factors that can affect the rate of a given reaction; the nature of the reactants is not the only factor that affects the rate of reaction. Temperature, for example, is an important factor for determining the rate of reaction. Generally speaking, higher temperatures cause reactions to progress more quickly by providing more energy for the chemical system. The concentration of the reactants is also an important determining factor for reaction rate. Higher concentrations of reactants cause the reactants to collide with each other more frequently, thereby increasing the rate at which they react with each other.
One of the most important factors in the determination of the rate of reaction, particularly in biological systems, is the presence of a catalyst. Catalysts are molecules that increase the rate of reaction without being consumed by the reaction. They do so by lowering the activation energy that a reaction must overcome in order to progress. A certain amount of energy is required before a reaction is allowed to go to completion, and catalysts decrease this amount of energy. Enzymes are biological proteins that are absolutely essential to most life, as many important chemical reactions that occur in animals would progress much too slowly without this catalyst.
Many mathematical methods have been developed to predict and to model the rate of a chemical reaction. These calculations are generally based on the concentration of the various reactants, the presence and precise nature of a catalyst, and the temperature, though other factors may also be considered. Some experimental data is generally needed to accurately determine an equation that can be used to predict the rate of reaction at any point. Generally speaking, chemical kinetics, rate of reaction, and the mathematics associated with them are taught in high school and college chemistry.
I always make sure my students know that reactions are happening all over the place and that the rate can vary by a tremendous amount.
For example, metal rusting is a slow reaction between oxygen and iron, while adding baking soda and vinegar together is a fast reaction.
For the younger kids I use baking soda and hot syrup to show them how it fluffs up.
Then, they will really enjoy the lesson, since it can then be used to make peanut brittle.
I remember when we were taught about this in high school chemistry. I can't remember what substances we were adding together to create a reaction though.
We had to conduct experiments to see what helped the average rate of reaction move faster, or slowed it down. Warming the liquids slightly was one of our tasks, and also adding a catalyst.
It was a cool lesson, especially since the teacher didn't tell us what to expect beforehand. I think he got us all to read the chapter on it afterwards so that we could put what we learned into context.
Personally, I think letting kids discover science as though for the first time is the way to go.