Question

Assertion :

In the first step of Ostwald's process for synthesis of nitric acid, ammonium is oxidised to $NO$ by the reaction $4N{H}_3\left(g\right)+5O_2\left(g\right)\rightleftharpoons 4NO\left(g\right)+6H_{2}O\left(g\right)$, $\Delta H^{\circ }=-905.6kJ$

The equilibrium amount of $NO$ will be less with increase in temperature. Reason: Heat is absorbed by products on increasing the temperature and the equilibrium shifts towards left.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Oswald process is used to create nitric acid as per following steps,
Step 1:
$4N{H}_3$ (gas) + $5O_2$ (gas) $\to$ $4NO$ (gas) + $6H_{2}O$ (gas)
In this step, ammonia is heated with oxygen. This yields nitric oxide ($NO$) and water as products.
Step 2:
$2NO$ (gas) + $O_2$ (gas) $\to$ $2N{O}_2$ (gas)
In this step the nitric oxide ($NO$) that was created in the first is combined with oxygen again to create nitrogen dioxide ($N{O}_2$).
Step 3:
$3N{O}_2$ (gas) + $H_{2}O$ (liquid) $\to$ $2HN{O}_3$ (aqueous solution) + $NO$ (gas)
In this step, the nitrogen dioxide is absorbed with water to create nitric acid (HNO3) as an aqueous solution. This also yields nitric oxide (NO).
Step 4:
$4N{O}_2$ (gas) + $O_2$ (gas) + $2H_{2}O$ (liquid) $\to$ $4HN{O}_3$ (aqueous solution)
For this last step, the nitric oxide created along with the nitric acid is recycled and combined with oxygen and water to create a higher concentration of nitric acid ($HN{O}_3$).
This reaction is exothermic because, during the process, it releases heat.
In reference to Le chatelier's principle, since this reaction is exothermic, conditions that would favor the forward reaction and shift the equilibrium to the right would be decreasing the temperature, increase the concentration, and increase the pressure and volume.
Thus option A is correct.