Ammonia

Why study ammonia?

Why is ammonia used in fertilisers? it provides nitrogen for plants to make plant proteins necessary for growth and repair of plant cells nitrogen fertilisers promote plant growth and increase crop yields

Nitrogenous Fertilisers most plants are unable to make use of atmospheric nitrogen (79%) directly plants get nitrogen supply by absorbing soluble nitrogen compounds from the soil Examples: ammonium nitrate, ammonium sulfate, urea CO(NH2)2

Reversible Reaction reactions that can go either direction forward and backward reactions take place at the same time

Reversible Reaction do not go into completion reactions achieve equilibrium[equilibrium is achieved when amounts of reactants and products no longer change] a mixture of reactants and products at the end of the reaction amounts of reactants and products at equilibrium can be changed by altering conditions [e.g. temperature and pressure]

The Haber Process invented in 1908 by Fritz Haber originally used to make explosives soon became the main source of ammonia to make nitrogen fertilisers

The Haber Process

Effect of conditions on the yield of ammonia temperature A lower temperature increases the yield of ammonia. However, a lower temperature also results in a slower reaction.

Effect of conditions on the yield of ammonia pressure A greater pressure increases the yield of ammonia, as well as the rate of reaction. However, maintaining higher pressure is costly and involves a safety risk.

Conditions for Haber Process temperature of 450 C pressure of 250 atm presence of iron catalystfor maximum yield of ammonia

An undesirable effect is produced when calcium hydroxide is added to the soil together with a nitrogenous fertiliser.

Explain why it is not advisable to do so.

Displacement of Ammonia from its SaltsHeating an ammonium salt with an alkali displaces the ammonia from the salt.

2NH4Cl(s) + Ca(OH)2 (aq) CaCl2 (aq) + 2NH3(g) + H2O(l)

ammonia is used widelymost importantly in the production of fertilisers, which affects our food crops

*other than nitrogen, phosphorus and potassium are also essential plant nutrients

when crops are harvested, plant nutrients are removed from soil. they need to be replaced otherwise they will run out. it will affect the amount and quality of crops in the future. *the fertilisers supplies ammonium ionsammonium ions are rapidly oxidised to nitrate ions in soil

*as soon as ammonia is formed from nitrogen and hydrogen, some of it is converted back to nitrogen and hydrogen.*at equilibrium the reaction do not stop, they proceed in both directions at the same speed. hence maintainng a constant amount of reactants and products*nitrogen from fractional distillation of air hydrogen from cracking of petroleum

nitrogen and hydrogen do not react in air. strong covalent bonds in nitrogen molecule. therefore the need for higher pressure and temperatures.

delta H = -184kJ exothermic reaction gives out heat

*the haber process was invented in 1908 to make explosives. but soon became the main source of ammonium for making fertilisers.

the need for conditions: strong covalent bonds between nitrogen atoms in nitrogen gas.

the higher the temperature the smaller the percentage of ammonia at equilibriumthe higher the pressure the greater the percentage of ammonia at equilibrium**