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 catalyst

for 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 Salts

Heating an ammonium salt with an alkali displaces the ammonia from the salt.

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