Chemistry - Thermochemistry Question with Solution | TestHub

The question asks to identify the incorrect statements.

Statement C is incorrect. Spontaneity of a reaction is determined by the change in Gibbs free energy ($\Delta G$), not solely by enthalpy ($\Delta H$). The relationship is $\Delta G=\Delta H-T\Delta S$. An endothermic reaction ($\Delta H>0$) can be spontaneous if the entropy change ($\Delta S$) is sufficiently positive and the temperature ($T$) is high enough (e.g., melting of ice at $T>0$ °C).

Statement D is incorrect. Extensive properties depend on the amount of matter (e.g., volume, mass, internal energy). Intensive properties do not depend on the amount of matter (e.g., pressure, temperature, density). Therefore, pressure and temperature are intensive properties, while volume is an extensive property.

Statements A and B are correct.

A. Graphite is the standard state for carbon, so its enthalpy of formation is defined as 0. Diamond has a positive enthalpy of formation (approximately $+1.897$ kJ/mol), meaning graphite is more stable and has a lower enthalpy.

B. The enthalpy of formation of liquid water, $\Delta H_f^{\circ }({\mathrm{H}}_2\mathrm{O}(\mathrm{l}))$, is more negative (around $-285.8$ kJ/mol) than that of gaseous water, $\Delta H_f^{\circ }({\mathrm{H}}_2\mathrm{O}(\mathrm{g}))$ (around $-241.8$ kJ/mol). This is because energy is released when gaseous water condenses to liquid water.

The final answer is $\boxed{C,D}$.