Question

Formation of $\text{NO}_{2(g)}$ from $\text{N}_{2(g)}$ and $\text{O}_{2(g)}$ is an endothermic process. Which of the following is true for this reaction?

• A. $\Delta H = 0$
• B. $\Delta H \lt 0$
• C. $\Delta H = \Delta U$
• D. $\Delta H \gt 0$

Hint:

Do not spend valuable time computing things like $\Delta n_g$ or comparing $\Delta H$ and $\Delta U$ using $\Delta H = \Delta U + \Delta n_g RT$ unless absolutely necessary. The term "endothermic" strictly and fundamentally dictates that $\Delta H \gt 0$ under any circumstances.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The problem states that the formation of NO₂ from N₂ and O₂ is endothermic and asks for the corresponding sign of ΔH.

Step 2: Key Formula or Approach:
An endothermic reaction absorbs heat from the surroundings, which thermodynamically corresponds to a positive enthalpy change (ΔH>0).

Step 3: Detailed Explanation:
Since the synthesis of NO₂ gas requires an input of energy, the enthalpy of the system increases. Therefore, the change in enthalpy (ΔH) for this process is greater than zero.

Step 4: Final Answer:
For an endothermic process, ΔH>0, which is represented by option (D).