The Rate and Extent of Chemical Change: Rate of Reaction
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What are the two formulae to calculate rate of reaction?
quantity of products formed ————————————— time taken (s) quantity of reactants used ————————————- time taken (s)
What are the factors that affect the rate of chemical reactions?
• temperature • concentration/pressure • surface area • presence of catalyst
What does collision theory state?
In order for particles to react they must collide with one another with suffiecient energy. This energy required it called the activation energy.
How does increased temperature increase the rate of reaction?
• as temperature increases, the particles gain more energy • this means they’ll move faster • therefore they will collide more frequently • they will also collide with more energy due to point 1 • this means they’re more likely to exceed the activation energy • therefore overall there will be a higher rate of successful collisions • and so a higher rate of reaction
How does increased concentration/pressure affect the rate of reaction?
• there are more particles per unit volume • more frequent collisions • increases rate of reaction
How does increased surface area affect the rate of a reaction?
• an increased surface area : volume ratio means increased rate of reactiom • this is due to there being a larger area over which collision could take place • this means the frequency of the collisions is higher
What are catalysts?
Substances that speed up a reaction without being used up the reaction themselves.
How does the presence of a catalyst increase the rate of reaction?
• a catalyst lowers the activation energy by providing an alternative reaction pathway • this means there will be a higher proportion of successful collisions
What metals are frequently used as catalysts?
transition metals