N2(g) + 3H2(g) <--> 2NH3(g) + 92 kJ.
Below is a diagram of an iron oxide catalyst used in industries to produce ammonia economically.
| Periodic Table | Haber Process Steps | |
| Rejected Periodic Table | Kangen Water |
The Haber Process is a method of producing ammonia
developed in WWI. The Germans needed nitrogen
to for making their explosives. When the Allies blocked off all trade
routes going to and from Germany, they lost all source of sodium
nitrate and potassium nitrate, their
source of nitrogen. They found their
source of nitrogen in the air, which was 80%
nitrogen. The chemist Fritz Haber developed
the Haber Process in WWI, which takes molecular nitrogen
from the air and combines it with molecular hydrogen
to form ammonia gas, which the chemical formula
is NH3.The equation for
the reversible reaction is:
N2(g) + 3H2(g)
<--> 2NH3(g) + 92
kJ.
Below is a diagram of an iron oxide catalyst used in industries to produce
ammonia economically.
When a reaction is reversible, the reaction can go
either forwards or backwards.
The FORWARD reaction is the reaction that we want,
where the reactants are converted into products. The BACKWARD reaction
is where the products become the original reactants. The reactions of
both occur at the same time.
In a CLOSED system the equilibrium mixture after
awhile is reached, where a specific proportion of the mixture exists as
reactants and the rest as products. A CLOSED system is where none
of the reactants or products can get out into the outside environment.
When equilibrium has been reached
it doesn't mean that the reactions have stopped. It means that the
FORWARD reaction is making products in the same amount as the BACKWARD
reaction is making reactants. This is called a DYNAMIC equilibrium.
Dynamic means moving or changing, to tell you that the reaction is till
reacting.
For a reversible reaction, Le Chatelier's Principle states that
"The equilibrium position will respond
to oppose a change in the reaction conditions".
Which means that is a product is removed then the equilibrium balance changes to make more of the product. The substance then tries to go back it's original equilibrium. then it repeats the process until nothing of the original substance is left. This is very useful. The reverse is also correct if you remove a reactant, the equilibrium will adjust to make more reactant, this is not useful.
Heat may be treated as reactant (an exothermic reaction)
or a product (an endothermic reaction).
If heat is REMOVED from an exothermic reaction (cool
it down) more product will be produced because the equilibrium will shift
to produce it. This will produce heat and also more chemical product
that you want in the equilibrium mixture.
If heat is ADDED to an exothermic reaction (raise
it temperature) the reverse will happen and less product will be produced
in the equilibrium mixture.
For a reversible reaction involving gases.
INCREASING the pressure will shift the equilibrium
towards the side of the reaction, which has the smaller volume.
DESCREASING the pressure will shift the equilibrium
towards the side of the reaction that has the larger volume.
The industrial conditions for producing ammonia
the
temperature must be 450ºC to 500ºC. The FORWARD reaction
(to form ammonia) is exothermic (it gives
out heat).
If we remove heat as a product (cooling the reaction
down) will result in the equilibrium mixture making richer ammonia.
(See
La
Chatelier's
Principle)
Since we want ammonia
from the Haber Process, why is the reaction conducted
at 450ºC? Because all reactions go faster if the temperature
is raised.
Reversible reactions, such as the Haber Process,
RAISING the temperature will make the equilibrium mixture richer in nitrogen
and hydrogen because forming these from ammonia
takes heat in. If we COOL the reaction down the proportion of ammonia
will increase but the rate of production will decrease. (because the temperature
is LOWER).
It's no good to have 90% ammonia
if it takes all day to fill a bucket full, than to have 10% ammonia
very quickly, having thousands of liters by the end of the day.
Ammonia is produced
at the atmospheric pressure of 100 atm because it is too expensive to
make a high-pressure chemical plant. Running the reaction at 200
atm is the highest pressure with the greatest return value.
With a reversible reaction, a catalyst which increases
the rate will increase the rate of both the forward and the backward reaction.
This is useful because the catalyst will, cause the reaction mixture to
reach its equilibrium composition more quickly. The catalyst will
not change the equilibrium composition of the substance. To see a
diagram of a catalyst click on the link (catalyst diagram).
The overall reaction is
ammonia
+ oxygen
± nitric acid
+ water.
4NH3(g)
+ 8O2(g)
± 4HNO3(aq)
+ 4H2O(l)
Ammonium
Nitrate
Ammonium
Nitrate is the main fertilizer used.
This is created by reacting nitric acid
and ammonia.
nitric
acid +
ammonia
± ammonium nitrate.
HNO3(aq)
+ NH3(g)
± NH4NO3(aq)
Ammonia with sulphric acid would create ammonium sulphate.
ammonia
+ sulphric acid
± ammonium sulphate.
NH3(g)
+ HSO4(aq)
± (NH4)2SO4(aq)
Ammonium nitrate has a higher percentage of nitrogen than ammonium sulphate, for the same amount of mass of fertilizer.
Environmental
Issues
The
benefits of using a nitrogenous fertilizers is obvious because the crops
grow taller, and are healthier therefore yielding a higher crop and therefore
cheaper, more plentiful food.
There are always disadvantages.
These are after applying the fertilizer and it rains or too much fertilizer
is used it gets into the steams or rivers and pollutes them. In the
rivers, the fertilizer does the same as it would on land, the river plants
grow and algae grow rapidly because of the abundant food supply.
The algae then die in large numbers. The bacteria feeding on the
dead plant material use up the oxygen
in the water.
Fish may then die because of the lack of oxygen
in the water.
Also too high of nitrates in the drinking water
is a health hazard, particularly with infants. Nitrates can interfere
with the oxygen
flow in the blood stream.