State how —

(i) a higher ratio of the reactant air

(ii) exothermicity of the catalytic reaction

(iii) use of low temp. in the conversion of NO to NO₂ — affects each related step in Ostwald's process.

(i) Air is used in all the three main reactions of Ostwald's process i.e., the reaction in the catalytic, oxidation and absorption tower including oxidation of nitric oxide to nitrogen dioxide which requires excess of air. Hence, a higher ratio of the reactant air is used.

(ii) Since the reaction is exothermic in nature, the electrical heating is done initially only. The heat evolved i.e., heat of reaction further maintains the required temperature of the reaction.

(iii) Low temperatures are used since they :

• Facilitate easy oxidation of nitric oxide to nitrogen dioxide
• Minimize the chances of any decomposition of nitrogen dioxide which may take place at higher temperatures.