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The Haber Process
The Haber process
is used to makeammonia NH3
Uses of ammonia include:
Making fertilisers Making nitric acid Making nylonThe equation
for the reaction is:
N2 + 3H2 2NH3 H = -92 kJ mol-1
The forward reaction would be favoured by a lowtemperature
because the forward reaction isexothermic (so lowering the
temperature would cause
the reaction to make more NH3 to heat things up abit
more). 450C isnt a low temperature. It is however, a
compromise temperature, because if the temperature
was made to be low, the reaction would be so slow
that it would take a very long time to produce much
ammonia.
Pressure is also another compromised. Because theforward
reaction has less molecules than the back
reaction (2 molecules of NH3 as opposed to 1 N2 and 3
H2 molecules), the forward reaction would be
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favoured by a high pressure. 200 atm is high, but
anything higher would be extremely expensive.
The iron catalyst speeds the reaction up but has noeffect on the
equilibrium. However, if the catalyst
wasnt used, the reaction would be too slow.
The Contact Process
1.Burn sulphur in air to formsulphur dioxide SO2
S + O2 SO2
2.Use an excess of air to reactsulphur dioxide to more oxygen
to
form sulphur trioxide
2SO2 + O2 2SO3 H =
-196 kJ mol-1
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3.Reacting sulphur trioxide with water will give
anuncontrollable fog of concentrated sulphuric acid.
Instead, sulphur trioxide is absorbed in concentrated
sulphuric acid to give fuming sulphuric acid (oleum):
SO3 + H2SO4 H2S2O7
4.This is converted into twice as much concentratedsulphuric
acid by careful addition of water:
H2S2O7 + H2O 2H2SO4
The reversible reaction here is:
2SO2 + O2 2SO3 H = -196 kJ mol-1
Because the forward reaction is exothermic, a lowtemperature has
to be used. Again, if a lowtemperature is used, the rate of
reaction would be too
slow, so 450C is a compromise.
As for the pressure, a low pressure is needed becausethe forward
reaction contains fewer molecules than the
back reaction.
The catalyst, vanadium (V) oxide (V2O5) speeds upthe rate of
reaction but has no effect on the
equilibrium. Again, without a catalyst, the rate of
reaction would be extremely slow.
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Uses of sulphuric acid include:
Making fertilisersincluding ammonium sulphate andother
substances
Detergentsincluding hand soaps and shampoos Paint
Manufactureused to extract titanium dioxide
from titanium ores
Tests for Gases
Gas Test Result
Hydrogen Hold a lit splint in presence
of hydrogen gas.
Produces a squeaky pop.
Oxygen Hold a glowing splint in
presence of oxygen gas.
Glowing splint relights.
CarbonDioxide
Bubble through limewater. Turns limewater fromcolourless to
cloudy,
milky white.
Ammonia Hold damp red litmus
paper in ammonia gas.
Turns damp red litmus
paper blue.
Chlorine Hold damp blue litmus
paper in chlorine gas.
Bleaches or turns blue
litmus paper white.
