COMEDK · Chemistry · 6. Thermodynamics (C)

The enthalpy of the reaction,
\(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(g)\) is \(\Delta H_{1}\) and that of \(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)\) is \(\Delta \mathrm{H}_{2}\). Then

A \(\Delta H_{1}>\Delta H_{2}\)
B \(\Delta H_{1}=\Delta H_{2}\)
C \(\Delta H_{1} < \Delta H_{2}\)
D \(\Delta H_{1}+\Delta H_{2}=0\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(\Delta H_{1} < \Delta H_{2}\)

Step-by-step Solution

Detailed explanation

\(\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(g) ; \Delta \mathrm{H}_{1}=+\mathrm{ve}\) \(\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \quad ; \Delta \mathrm{H}_{3}=+\) ve…

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.

Same subject

Match the names of reactions given in Column I with the appropriate reactions given in Column II.

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No.	Name of reaction	No.	Equations representing reactions
A	Sandmeyer	P	\(2C_6H_5Cl + Na\) (dry ether) \(\to\) Diphenyl
B	Fittig	Q	\(CH_3 - CHBr - CH_3 + AgF \to CH_3 - CHF - CH_3 + AgBr\)
C	Swarts	R	\(CH_3 - CH_2 - Br + NaI\) (Acetone) \(\to CH_3 - CH_2 - I + NaBr\)
D	Finkelstein	S	\(C_6H_5N_2^+ Cl^- + Cu_2Br_2/HBr \to C_6H_5Br + N_2\)

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The enthalpy of the reaction,\(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(g)\) is \(\Delta H_{1}\) and that of \(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)\) is \(\Delta \mathrm{H}_{2}\). Then

Step-by-step Solution

The enthalpy of the reaction,
\(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(g)\) is \(\Delta H_{1}\) and that of \(\mathrm{H}_{2}(g)+1 / 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)\) is \(\Delta \mathrm{H}_{2}\). Then