Question

Which one of the following reactions has
\(\Delta H = \Delta U\)?

• A. \( C_6H_6 (l) + \frac{15}{2} O_2 (g) \to 6CO_2 (g) + 3H_2O (l) \)
• B. \( 2HI (g) \to H_2 (g) + I_2 (g) \)
• C. \( N_2 (g) + 3H_2 (g) \to 2NH_3 (g) \)
• D. \( CaCO_3 (s) \to CaO (s) + CO_2 (g) \)

Hint:

When reactions involve only solids or liquids, or when there is no change in the number of moles of gases, \(\Delta H\) is equal to \(\Delta U\).

Answer 1

The Correct Option is B

In the reaction where there is no change in the number of moles of gases or phase change, the enthalpy change (\(\Delta H\)) is equal to the internal energy change (\(\Delta U\)) as no work is done (\(w = 0\)) in such cases. In Option 2, the reaction is occurring between gaseous reactants and products without phase changes, and thus \(\Delta H = \Delta U\).