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Collision theory
· For a reaction to take place
between 1 particles, they must
collide and do so with enough
energy to break the bonds and in
the correct orientation.
· Not all collisions are successful
because not all particles have the
activation energy.
Rate of reactions
· The rate of a chemical reaction
increases when you
­ Increase the temperature
­ Increase the concentration of a
­ Increase the pressure of a gas
­ Increase the surface area of solid
­ Use a catalyst…read more

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The Maxwell - Boltzmann distribution
· The area under the graph represents the total number
of particles and stays the same whatever the
· Ea is the activation energy. Only collisions occurring
with more than this energy result in reaction.
· Increasing the temperature increases the number of
collisions occurring above the activation energy.
· The change from blue to red is only an increase in
temperature of 10°C, however the number of particles
that have enough energy to react has increased
significantly…read more

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Catalysts are substances that affect
the rate of chemical reactions
without being chemically changed
themselves. Catalysts are usually
used to speed up reactions. They
work by providing a different
pathway for the reaction, one with a
lower activation energy. Catalysts
do not affect the enthalpy change of
reactions, nor do they affect the
position of equilibrium in a
reversible reaction.…read more

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Reaction catalyst type use
N2(g) + 3H2 (g) 2NH3(g) iron heterogeneous Making
Haber process fertilisers
4NH3 + 5O2 4NO + 6H2O Platinum and heterogeneous Making
Ostwald process for making nitric acid rhodium fertilisers
H2C=CH2 + H2 CHcCH3 nickel heterogeneous Making
Hardening of fats with hydrogen margarine
Cracking hydrocarbon chains from Aluminium heterogeneous Making
crude oil oxide petrol
Catalytic converter reactions in car Platinum and heterogeneous Removing
exhausts rhodium polluting
H2C=CH2 + H2O CH3CH2OH H+ absorbed heterogeneous Making
Hydration to produce ethanol on solid silica ethanol- a
Phosphoric fuel additive,
acid solvent and
(H3PO4) chemical
CH3CO2 (l) + CH3OH (l) H+ homogeneous Making
CH3CO2CH3 (aq) + H2O (l) solvents
esterification…read more

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Different catalysts work in different ways. There are two
­ Heterogeneous catalysts
· The catalyst is in a different phase to the reactants
­ Homogenous catalysts
· Where the catalyst and reactants are in the same phase
Catalytic converters
· These reduce the levels of a number of polluting gases
· The catalytic converter is a honeycomb (increases
surface area), made of ceramic material coated with
platinum and rhodium metals- the catalysts.
· As they pass over the catalyst, the polluting gases react
with each other to form less harmful products by the
following reactions
­ Carbon monoxide + nitrogen oxides nitrogen and
carbon dioxide
­ Hydrocarbons + nitrogen oxides nitrogen + carbon
dioxide + water
· The reactions take place on the surface of the catalyst
in 2 steps:
1. The gases first form weak bonds with metal atoms of the
catalyst, (adsorption) this holds the gases in just the right
position for them to react together, the gases then react
on the surface
2. The products then break away from the metal atoms; this
process is desorption. This frees up room, on the catalyst
surface for more gases to take their place and react.
· The strength of the weak bonds holding the gases onto
the metal surface is critical. They must be strong
enough to hold the gases for long enough to react, but
weak enough to release the products easily.…read more

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