Cycles -Nitrogen cycle -exercises

Lightning produces nitric oxide

N_2(g) + O_2(g) --> 2NO_(g)

Further reaction with oxygen produces nitrogen dioxide which late reacts with water to produce nitric acid according to the reaction below.
2NO_2(g) + H₂O_(l) => HNO_3(aq) + HNO_2(aq)

Proteins are degraded by aerobic bacteria into carbon dioxide, water and ammonia according to the reaction below.

2CH₂NH₂COOH + 3O₂ => 4CO₂ + 2H₂O + 2NH₃

This is decomposition of organic matter in the presence of oxygen(aerobic).

Denitrifying bacteria return nitrogen back to the atmosphere. These bacteria are anaerobic (do not require oxygen) and convert nitrogen compounds to nitrogen gas.

NH₄NO₃ => N₂ + H₂O + O₂

Urea from animal waste is acted on by bacteria and converted into ammonia and carbon dioxide according to the reaction below.

NH₂CONH₂ + H₂O => 2NH₃ + CO₂

You may have forgotten some sweaty clothes in the car on a hot day only to come back to a strong smell of ammonia. The urea in the sweat is broken down with the help of enzymes by bacteria

The Haber process is an industrial process that fixes nitrogen. It converts atmospheric nitrogen into ammonia according to the reaction below.

N₂ + 3H₂ => 2NH₃

Ammonia is later used, largely, for the production of fertilisers.

Elemental nitrogen N₂ has an oxidation state of 0

Nitrogen cycle exercises

1) What is the oxidation state of nitrogen in the atmosphere?

2) Below are several equations, match the equations to one of the steps in the diagram above.

a) N₂ + 3H₂ => 2NH₃

b) 2CH₂NH₂COOH + 3O₂ => 4CO₂ + 2H₂O + 2NH₃

c) NH₂CONH₂ + H₂O => 2NH₃ + CO₂

d) N₂ + O₂ => 2NO

e) 2NO₂ + H₂O => HNO₃ + HNO₂

f) NH₄NO₃ => N₂ + H₂O + O₂

Pass the cursor over each step to show the solutions.

The main pathways by which conversions of nitrogen take place in the nitrogen cycle are listed below.
1 ) N₂ => NH₃ => NH₄⁺

2) N₂=> NO => NO₂ => NO₃

3) NO₃^- => N₂O => N₂
4) NH₃/NH₄⁺=> NO₂ => NO₃^-

For each of the statements in the following table, complete the column under each of the pathways (1 to 4) relevant to that statement. Note that each statement may refer to more than one pathway.

pathway(s) involving nitrogen fixation

pathway(s) involving soil bacteria

pathway(s) in which nitrogen atoms undergo reduction

pathway(s) showing reaction(s) caused by lightning strikes

Solution

pathway(s) involving nitrogen fixation	1 and 2
pathway(s) involving soil bacteria	1, 3 and 4
pathway(s) in which nitrogen atoms undergo reduction	1 and 3
pathway(s) showing reaction(s) caused by lightning strikes	2
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