Chemistry - Thermochemistry Question with Solution | TestHub

Question Explanation:

Match the relation of $\Delta H$ and $\Delta U$ for given reactions.

Concept:

This question is based on Hess's law, specifically the relationship $\Delta H=\Delta U+\Delta n_{gas}\cdot RT$.

Solution:

Use $\Delta n=(molesgasproducts-molesgasreactants)$ and $\Delta H=\Delta U+\Delta n\cdot RT$.

1. H₂(g) + Cl₂(g) → 2HCl(g): $\Delta n=2-2=0$ $\Rightarrow \Delta H=\Delta U$ (match Q).

2. 2N₂O(g) + O₂(g) → 2NO₂(g): $\Delta n=2-3=-1$$\Rightarrow \Delta H=\Delta U-RT$ (match S).

3. H₂(g) + I₂(s) → 2HI(g): $\Delta n=2-1=+1$ $\Rightarrow \Delta H=\Delta U+RT$ (match P).

4. N₂(g) + 3H₂(g) → 2NH₃(g): $\Delta n=2-4=-2$$\Rightarrow \Delta H=\Delta U-2RT$ (match R).

Final Answer: The correct option is (A)