Different
reaction rates Chemical reactions occur at different
rates.
The weathering of rocks such as limestone
is a very slow reaction which may take decades.
Rusting is a slow reaction which may
take years.
Cooking is a steady reaction taking no
more than two or three hours.
Explosions are incredibly fast reactions
which occur in less than a second.
2.
Factors
affecting reaction rates The rates of chemical reactions are
affected by:
surface area
concentration
temperature
catalysts
3.
Measuring
reaction rates
During a reaction, reactants are being
used up and products are forming.
We can use these changes to measure the reaction
rate.
Reaction rate
4.
Explaining the effect
of different factors on reaction rates Chemical reactions occur when particles
of the reacting substances collide.
This is called the collision theory.
The diagram below uses the collision theory to explain how
different factors affect the reaction rate.
5.
Catalysts and enzymes
Catalysts
are substances which speed up chemical reactions without
being used up. They can take part in the reaction over and
over again.
Catalysts are vital for many industrial
processes including the production of ammonia, sulphuric
acid and petrol. The catalysts for many industrial processes
are transition metals or their compounds.
Catalysts speed up reactions by helping
substances to react more easily.
They do this by allowing bonds in the reactants to break
more readily and new bonds to form more easily.
The catalysts for biological processes
are called enzymes. Almost
every chemical reaction in living things has its own particular
enzyme.
Enzymes are denatured
at temperatures above 40 °C. Denaturation
involves a change in the structure of the enzyme which makes
it less efficient.
Enzymes are important in baking, brewing,
cheese-making and in the manufacture of yoghurt, fruit juices
and vitamins.
