AmmoniaAmmonia

Darryl Ho 4L04

• A chemical compound (NH3)

• Colorless gas with strong pungent odor

• Highly soluble in water

• Non-flammable

• Toxic by inhalation

Ammonia

Uses of Ammonia• Ammonia is most commonly used as fertilizers. Ammonia (NH3) consists of

nitrogen, essential for plant growth.

• Ammonia & Ammonium ions (NH4+)

are converted into nitrates by soil bacteria, which are then absorbed by the plants for nitrogen.

• Examples: Anhydrous Ammonia, Ammonium Nitrate and Ammonium Sulphate

• Weak ammonia solutions are also widely used as commercial and household cleaners and detergents.

Modern Ammonia Production (The Haber Process)

Achieved by the direct combination of hydrogen and nitrogen, over an iron or aluminium catalyst. Hydrogen is obtained from the decomposition of methane by heating. Nitrogen is obtained from the distillation of liquefied air. The reaction is shown below:

N2(g) + 3H2(g) 2NH⇌ 3(g)

Fertilizer (Ammonium Nitrate)

• Ammonia is a thermally unstable compound.

• It has a melting point of 169ºC.

• Ammonia can result in an endothermic reaction or an exothermic reaction, depending onenvironmental factors such as the pH, confinement and temperature.

• Since Ammonium nitrate is a thermally unstable compound, it produces a large amount of heat

during exothermic decomposition.

• During decomposition, it also produces a large volume of oxygen gas for combustion of other fuels.

Fertilizer (Ammonia Nitrate)

• When carried out in a closed system under low temperature,

• Endothermic dissociation of NH4NO3 into NH3 and HNO3 takes place [a reversible reaction].

• Ammonia is not allowed to escape the system• There is no change in the pH of the environment

and the amount of ammonia in the system.

NH4NO3 NH3 + HNO3 [ΔH > 0]NH4NO3 NH3 + HNO3 [ΔH > 0]

Fertilizer (Ammonium Nitrate)

• When carried out in a opened system under a high temperature,

• Endothermic dissociation of NH4NO3 into NH3 and HNO3 takes place initially.• However, ammonia escapes the system when produced.• A decrease in the pH of the environment and increase in

temperature enhances the exothermic decomposition of NH4NO3

(below)

• Since a large net amount of heat is released during the decomposition, ammonium nitrate can be used as an

explosive material.

Fertilizer (Explosive)

NH4NO3 NH3 + HNO3 [ΔH > 0]NH4NO3 NH3 + HNO3 [ΔH > 0]

2NH4NO3 2N2 + 4H2O + O2 [ΔH = -1460 kJ/kg]2NH4NO3 2N2 + 4H2O + O2 [ΔH = -1460 kJ/kg]

• During the exothermic decomposition of NH4NO3,

the NO3- ions oxidize the NH4

+ ions in N2O

• N2O,decomposes into N2 and O2 under high temperature, producing a large amount of gas.

• A large amount of the oxygen gas produced is used for the combustion of other fuels mixed with the fertilizer

• This causes the fuels to combust at a faster rate and produce more heat for the exothermic decomposition

of NH4NO3.

Fertilizer (Explosive)

2NH4NO3 → 2N2 + 4H2O + O2 [ΔH = -1460 kJ/kg]2NH4NO3 → 2N2 + 4H2O + O2 [ΔH = -1460 kJ/kg]

Endothermic

NH4NO3 NH3 + HNO3

Closed System / Low Temperature

ExothermicFuel

Combustion

Open System / High TemperatureNH3 leaves system

N2O + H2O

Combusting FuelCombusting

Fuel

Exothermic

N2 + O2 + H2O

N2 + O2 + H2O

Exo

ther

mic

More oxygen available for combustion of fuel

Higher Temperature

Higher rate of exothermic decomposition

of NH4NO3

EXPLOSION

Why would terrorists use fertilizers ?

• Fertilizers (Ammonium Nitrate)

are explosive materials• Easily available and obtainable

• Not easily detectable (can pass through metal

detectors undetected)

• Soluble in water (easy to avoid detection)

A Terrorist’s Arsenal

For something intended as a gift of life to be used for destructive purposes is truly a tragedy.

The End