Chemistry - Thermochemistry Question with Solution | TestHub

Question Explanation:

Identify the correct statement(s) regarding thermodynamic stability, reaction enthalpy, and standard states.

Concept:

Enthalpy Definitions, Stability, and $\Delta \mathrm{H}/\Delta \mathrm{U}$ relation.

Solution:

Evaluate each statement based on thermodynamic principles.

(1)${\mathrm{CaCO}}_{3\text{ (calcite) }}\to {\mathrm{CaCO}}_{3\text{ (aragonite) }}$

$\Delta G=\left(-1127.75+1128.8\right)=+ve$

∴ Calcite more stable.

(2) In ${\mathrm{C}}_{(\mathrm{g})}+4{\mathrm{H}}_{(\mathrm{g})}\to {\mathrm{CH}}_{4(\mathrm{g})}$

No energy is required to break the bond.

∴ More energy release

(3)$\Delta {\mathrm{H}}_1^{\circ }{\mathrm{I}}_2(\mathrm{g})\Rightarrow {\mathrm{I}}_2(\mathrm{s})\to {\mathrm{I}}_2(\mathrm{g})=\Delta {\mathrm{H}}_{\text{sub }}^{\circ }$ of ${\mathrm{I}}_2(\mathrm{s})$

∴ (3) is correct.

(4)$\Delta H=\Delta U+RT(\Delta n)$

$\Delta U$ & $\Delta H$ are -ve $\Delta n_g$ is also-ve.

$$\left|\Delta \mathrm{H}\left|>\right|\Delta \mathrm{U}\right|$$

but with sign $\Delta \mathrm{H}<\Delta \mathrm{U}$