Describe the two known major natural mechanisms for converting atmospheric nitrogen to useable forms.

(a). Biological fixation

(b). Fixation by lightning

Explanation:

Gaseous nitrogen in the atmosphere has to be converted or "fixed" into a suitable form before it can be utilised by living organisms.

There two main ways of nitrogen fixation are

(a). Biological fixation: Majority (approximately 90%) of nitrogen fixation is carried out by bacteria. Bacterias such as Cyanobacteria transforms nitrogen into ammonium and ammonia : N2 + 3 H2 → 2 NH3. The produced ammonia can then be taken in directly by plants and /or the conversion products of ammonium and ammonia may further react in the process of nitrification.

(b). Fixation by lightning: Lightning energy causes the combination nitrogen (N2) and water (H2O) forming nitrates (NO3) and ammonia (NH3) . Rain water dissolves the formed nitrates and ammonia and the solution is drained into the ground, where they can be reached by plants plant roots for consumption.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years