Ammonia Flashcards

1
Q

raw materials in the haber process

A

air, methane, steam

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2
Q

how is nitrogen obtained?

A

Nitrogen is obtained by the fractional distillation of liquid air.

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3
Q

how is nitrogen obtained?

A

The hydrogen is obtained by the steam reforming of natural gas.
H2O + CH4 → CO + 3H2
CO + 3H2 + H2O → CO2 + 4H2

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4
Q

haber process

A

The nitrogen and hydrogen are mixed in the ratio 1:3.

This mixture is compressed to a pressure of 200 atm and passed over an iron catalyst at 500oC.

Under these conditions, there is 15% conversion of reactants into ammonia.

The gases leaving the catalysts consist of a small amount of ammonia and large amounts of unreacted nitrogen and hydrogen.

This mixture is passed through a CO system where the ammonia liquidifies and is extracted. The unreacted nitrogen and hydrogen is recycled for further conversion into ammonia.

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5
Q

uses of ammonia

A

To manufacture fertilisers
To manufacture nitric acid
To manufacture household cleaning agent
To manufacture pharmaceuticals

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6
Q

effect of temperature on haber process

A

The reaction is exothermic. Hence, the lower the temperature, the greater the yield of ammonia.
N2 + 3H2 ⇌ NH3

In the Haber process, very low temperatures can’t be used since the rate of production will be too slow, i.e. it takes a long time to get a high yield.
A compromise is made between the higher yield for a long time and smaller yields in a shorter time. Hence, the temperature of 500oC is chosen.

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7
Q

effect of pressure on the haber process

A

the reaction is accompanied by a decrease in volume. Hence, high pressures will increase the yield of ammonia.

A compromise is made between obtaining a high yield of ammonia at high pressures and high cost, and getting a smaller yield at lower pressure and lower cost. Hence, 200 atm is chosen.

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8
Q

why can’t very high pressures be used?

A

Very high pressures cannot be used since the cost of producing the ammonia will increase.
Stronger equipment
Higher wages
Safety measures

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9
Q

effect of Fe catalyst on the haber process

A

Catalyst does not increase the yield of ammonia. However, at lower activation energy, such that the yield is obtained in a shorter period.

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10
Q

benefit of using iron catalyst

A

the iron is porous so it presents a large surface area for gases to react on

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11
Q

effects of ammonia on the environment

A

eutrophication
smog
human health
soil acidification
changes to plant diversity

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12
Q

changes to plant diversity

A

Ammonia gas can settle on plant leaves and stems, and cause damage because of its alkalinity in alpine plants.

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13
Q

soil acidifcation

A

excess ammonium ions in fertilizers are converted to nitrates and hydrogen ions by bacteria
hydrogen ions make soil acidic so plants can’t grow well

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14
Q

effects on human health

A

Irritates lungs and inhibit uptake of oxygen by haemoglobin by altering pH of blood

Ammonia can react with acids in the atmosphere to form ammonium salts → particulates → can cause bronchitis, asthma and coughing fits when breathed in over time

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15
Q

smog

A

ammonia contributes with nitrogen and sulphur dioxides fromvehicles and infustry to form fine particles which make smog

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16
Q

eutrophication

A

Excess quantities of fertilisers pollute rivers and lakes → overgrowth of algae and bacteria → death of aquatic organisms

Rainwater dissolves fertilisers → solution leaches from fields to rivers and lakes → concentration of nitrates and phosphates in the water increases → algae uses the nutrients to grow very fast (algal bloom) → dense growth of algae blocks sunlight → plants and algae die → bacteria feeds on dead plants and algae to multiply rapidly → bacteria uses up oxygen → no oxygen for animals