Rates of Reaction
"Chemistry is the study of matter. But I prefer to see it as the study of change.” - Walter White, Breaking Bad.
This quote is from Breaking Bad is an excellent introduction to the science of Chemistry. Changes occur from Chemical Reactions, which occur when different particles combine, split up, or a bit of both. Chemical reactions allow everything from ourselves to the universe itself to be created.
What is a chemical reaction? Essentially, it is lots of small particles smacking into each other and causing a change to happen.
In National 5, you need to be able to follow chemical reactions from a start to an end point, and understand how reactants change to products.
Factors Affecting Reaction Rate
Temperature
An increase in temperature means that there is an increase in the kinetic energy of particles. This means that in a reaction, the particles are moving faster and thus collide with each other more frequently and with greater force. As there are more frequent collisions, an increase in temperature speeds up the rate of reaction.
Concentration
If you increase the concentration, this increases the amount of reactant (things that are reacting in the reaction), which allows a faster reaction as there are more particles involved.
Particle Size
A decrease in particle size increases the rate of reaction. If particle size is decreased, this creates a greater surface area. A larger surface area of reactants increases the chance of reactants colliding, therefore increasing the reaction rate.
Catalysts
A catalyst speeds up a chemical reaction without being used up in the reaction. They can be recovered at the end of reactions.
Catalysts
A catalyst speeds up a chemical reaction without being used up in the reaction. They can be recovered at the end of reactions.
Examples of catalysts to know in National 5 Chemistry include:
Iron is the catalyst in the Haber Process (the process used to produce ammonia)
Platinum is the catalyst in the Ostwald Process (the process used to produce nitric acid)
Biological catalysts are called Enzymes, which regulate chemical reactions in your body.
Calculating Reaction Rate
Reaction rate can be calculated using the given calculation:
Rate = change in quantity / change in time
The quantity may be mass, concentration, volume, etc. As long as you can calculate the change (difference) in quantity over time, you can calculate the reaction rate.
In the given graph we can see that line A and B represent the same chemical reaction occurring at different rates. Line A has a faster rate than B, however the same product is produced.
Key Points!
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Increasing Reaction Rate
To increase reaction rate:
Increase temperature
Increase concentration
Decrease particle size
Add a catalyst
Be able to explain why each of these factors have an affect on reaction rate.
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Catalysts
Catalysts speed up chemical reactions without being used up in the reaction.
Enzymes are biological catalysts.
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Calculating Reaction Rates
Be able to calculate the rate of reaction using the given equation and determine relative reaction rates from graphs.