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 $\Delta H/\Delta U$ relation.

Solution: Evaluate each statement based on thermodynamic principles.

(1) For the transformation ${\mathrm{CaCO}}_{3(calcite)}\to {\mathrm{CaCO}}_{3(aragonite)}$:

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

Therefore, calcite is more stable.

(2) In the reaction ${\mathrm{C}}_{(\mathrm{g})}+4{\mathrm{H}}_{(\mathrm{g})}\to {\mathrm{CH}}_{4(\mathrm{g})}$, no energy is required to break bonds, leading to a greater energy release.

(3) The enthalpy of sublimation for ${\mathrm{I}}_{2(\mathrm{s})}$ is represented by $\Delta H_1^{\circ }$ for ${\mathrm{I}}_{2(\mathrm{g})}\Rightarrow {\mathrm{I}}_{2(\mathrm{s})}\to {\mathrm{I}}_{2(\mathrm{g})}$. Therefore, statement (3) is correct.

(4) The relationship between $\Delta H$ and $\Delta U$ is given by $\Delta H=\Delta U+RT(\Delta n)$.

If both $\Delta U$ and $\Delta H$ are negative, and $\Delta n_{\mathrm{g}}$ is also negative, then:

$|\Delta H|>|\Delta U|$

However, considering the signs, $\Delta H<\Delta U$.