AP EAMCET · Chemistry · Thermodynamics (C)

If standard molar enthalpy change and standard molar internal energy change measured in bomb calorimeter are equal, which one of the following statements is correct?

A \(\Delta \mathrm{n}>0\), with increase in pressure
B \(\Delta \mathrm{n}>0\), with decrease in pressure
C \(\Delta \mathrm{n} < 0\), with increase in pressure
D \(\Delta \mathrm{n}=0\), at constant pressure

Verified Solution

Answer & Solution

Correct Answer

(D) \(\Delta \mathrm{n}=0\), at constant pressure

Step-by-step Solution

Detailed explanation

\(\Delta \mathrm{H}^{\circ}=\Delta \mathrm{U}^{\circ}\) (given) \[ \begin{aligned} & \Delta \mathrm{H}^{\circ}=\Delta \mathrm{U}^{\circ}+\mathrm{P} \Delta \mathrm{V} \\ & =\Delta \mathrm{U}^{\circ}+\Delta \mathrm{nRT} \\ & =\Delta \mathrm{U}^{\circ} \end{aligned} \]…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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