Q22.15P - Chemistry: Molecular Nature Of Matter And Change

Question

Nitrogen fixation requires a great deal of energy because the   bond is strong. 

(a) How do the processes of atmospheric and industrial fixation reflect this energy requirement? 

(b) How do the thermodynamics of the two processes differ? (Hint: Examine the respective heats of formation.) 

(c) In view of the mild conditions for biological fixation, what must be the source of the “great deal of energy”? 

(d) What would be the most obvious environmental result of a low activation energy for   fixation?

Step-by-Step Solution

Answer

(a) Lightning causes atmospheric fixation (and consequently large energy gain), whereas high temperature-pressure circumstances cause industrial fixation.

(b) Endothermic atmospheric fixation, exothermic industrial fixation.

(c) The root bacteria's enzyme lowers the activation energy for ${\mathrm{N}}_2$breakdown, resulting in a gentler biological fixation.

(d) One of the potential environmental disasters is eutrophication.

Step 1: Chemical energy

The energy held in the bonds of chemical compounds is known as chemical energy (molecules and atoms). It is produced as a by-product of the chemical reaction, which is known as an exothermic reaction.

Step 2: Subpart (a)

In the event of atmospheric ${\mathrm{N}}_2$fixation, energy is acquired through natural lightning. The endothermic reaction between ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$gases in the atmosphere produces nitric oxide $\mathrm{NO}$ causing the N-N bond to be broken after gaining $180.60\mathrm{kJ}$of energy. Later, the $\mathrm{NO}$is changed to ${\mathrm{NO}}_2$ and ${\mathrm{HNO}}_3$resulting in nitrate ion penetration into the soil and sea. In the Haber ammonia production process, the N–N bond is broken under high reaction conditions of $450°\mathrm{C}$ and $200\mathrm{atm}$pressure.

Therefore, atmospheric fixation by lightning and industrial fixation by high temperature-pressure circumstances.

Step 3: Subpart (b)

The enthalpy of $\mathrm{NO}$production while breaking the N–N bond is $180.6\mathrm{kJ}/\mathrm{mol}$ 

for atmospheric fixing. As a result, the reaction is endothermic, and energy (heat) is drawn from the environment.

The Haber’s process within the industrial fixation process, as seen in Chapter 17, has an enthalpy of 

$-91.8\mathrm{kJ}/\mathrm{mol}$. As a result, the reaction is highly exothermic, with heat being emitted into the environment.

Step 4: Subpart (c)

In the case of biological fixation, the root bacteria catalyse a multistep mechanism to decrease ${\mathrm{N}}_2$to ammonia. As a result of the use of a catalyst (in this case, an enzyme), the reaction's activation energy—that is, the minimum energy necessary to break the N–N bond—is reduced. As a result of the root bacteria's enzymes lowering the necessary energy barrier, biological ${\mathrm{N}}_2$ fixation happens at considerably gentler temperatures.

Step 5: Subpart (d)

If the activation energy of ${\mathrm{N}}_2$fixation was reduced, more nitrogen gas molecules would be broken apart. As a result, more N-containing compounds would be created, and N levels in the soil and sea would rise.

Excess nitrogen in the water, which acts as a fertiliser, can lead to eutrophication, in which more nutrients build in the water and soil. This would result in an excessive development of algae, which would cover the water's surface. As a result, there will be less oxygen available, fish will die, and the ecology will be ruined.