AmmoniaNH3

This is not the ammonia story:This is a story about ammonium nitrateWhy do we need ammonium nitrate?What chemicals do we need to make ammonium nitrate?Who played a part in the process development?What is the chemistry of the process including the Haberprocess?This isnt the only part of the learning:We will look at:

Reversible equilibriaLe Chateliers principlePercentage compositionNeutralisationBalancing equationsOxidation and reduction

Ammonium NitrateIn the first part of the twentieth century the Worlds abilityto produce food to feed an expanding population was in doubt.

Fertilisers with a source of nitrogen were known, such as caliche nitrates from South America, but these were gettingexpenses as resources ran out. Also, the concentration of nitrogen in these minerals was low.Chemists knew that if they could manufacture ammoniumnitrate, they would have a good source of nitrogen. However,an industrial method to make ammonia had not been foundand was essential to making both ammonium and nitrates.

Percentage CompositionElementAr

Mg24.3Na23.1N14.0O16.0H1.0Lets look at the nitrogen contents of:

Magnesium nitrateMg(NO3)2Sodium nitrateNaNO3Ammonium nitrateNH4NO3

% composition = ( nitrogen (by mass) / total mass (Mr) ) x 100Mg(NO3)2

NaNO3

NH4NO3

Mass N

Mr

% composition28.0

148.3

18.914.0

85.1

16.528.0

80.0

35.0

If we could make ammonia,how could we make ammonium nitrate?ammoniadissolves in waterto make

ammonium hydroxide(= ammonia solution)ammonia

is oxidised and thegas produced isdissolved in waterto make

nitric acidthese are neutralised to make

ammonium nitrateSo the World chemists knew the process, but how could theymake enough ammonia. This takes us to the start of the story.

The Haber ProcessFritz HaberWe know this process as the Haber Process,but in many parts of the world it is calledthe Haber-Bosch process in honour of oneof Habers colleagues who also helped in thedevelopment.Carl BoschN2(g) + 3H2(g) 2NH3(g)How do we get the nitrogen and hydrogen to Carry out this reaction?

How do we get them to react?

Remember, nitrogen is 78% of the air and very unreactive!

Raw materials for the Haber ProcessNitrogenHydrogenProduced in the reactionof methane and steam.From air: By burninghydrogen with oxygenin air, the remainder islargely nitrogen.

The Haber Processand Le Chateliers PrincipleLe Chateliers Principle states that whateveris done to a reaction, the reaction will act to oppose it. Example: If a product in an reversiblereaction is removed,more product will be produced to re-establish the equilibriumIt may be applied to pressure, temperatureand concentrations of reactants and products. Henri LouisLe Chatelier

Le Chateliers Principle states that whateveris done to a reaction, the reaction will act to oppose it. N2(g) + 3H2(g) 2NH3(g)Exothermic in theforward direction-92 kJ mol-11. Pressure. The amount of pressure exerted is proportional to thenumber of molecules. 4 molecules in the reactants, 2 molecules in the products. Increase the pressure and the reaction opposes it bymoving to reduce the pressure towards the products.2. Temperature. Increasing the temperature will always increase therates in both directions at equilibrium. This is an exothermic reaction.increasing the temperature will be opposed by moving towards thereactants in the endothermic direction. This needs to be a compromisebetween increased rate and low yield.3. Remove the products and the reaction will oppose the change bymaking more products.

N2(g) + 3H2(g) 2NH3(g)Exothermic in theforward direction-92 kJ mol-1Pressure: 200 atm (maximum safe pressure)Temperature: 450oC (compromise between rate and yield)Catalyst:Iron(used to increase the rate)Finally, the ammonia is removed in acondenser/cooler condensing it into aliquid. This removes the product andthe reaction acts to restore theequilibrium by making more.Unused gases are recycled.

Ammonium hydroxideAmmonia dissolves in water to make ammonium hydroxideNH3(g) + H2O(l) NH4OH(aq)Ions are formed in solution:NH3(g) + H2O(l) NH4+(aq) + OH- (aq)This the first reactant needed to make ammonium nitrate.

Nitric acid will be explained next.

Making nitric acidWrite a balanced reaction for thereaction between ammonia and oxygento form nitrogen monoxide (and water).Write a balanced reaction betweennitrogen monoxide and oxygen to form nitrogen dioxide.Write a balanced between nitrogendioxide, water and oxygen to makenitric acid.

Making nitric acidBalanced reaction for the reaction between ammonia andoxygen to form nitrogen monoxide (and water).Balanced reaction between nitrogen monoxide and oxygen to form nitrogen dioxide.Balanced reaction between nitrogen dioxide, water and oxygen tomake nitric acid.4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)Red hot Pt/Rh catalyst2NO(g) + O2(g) 2NO2(g)4NO2(g) + O2(g) + 2H2O(l) 4HNO3(aq)

Making ammonium nitrate by neutralisationNH4OH(aq) + HNO3(aq) NH4NO3(aq) + H2O(l)The salt is very soluble and is separated by evaporation.Ammonium nitrate is also very explosivewhen handled incorrectly and, as well asbeing a very effective fertiliser, it can beused as rocket fuel.In 2001, an ammonium nitrate explosionin Toulouse, France, caused several35 Deaths and over 500 homes to bedamaged.

The End Result