Chemistry - Thermochemistry Question with Solution | TestHub

$\mathrm{S}(s)+{\mathrm{O}}_2\to {\mathrm{SO}}_2$ is $-297\mathrm{kJ}$, so ${\Delta }_f{H}^{\circ }({\mathrm{SO}}_2)=-297kJ/mol$: (A) true.

${\mathrm{SO}}_2+\frac{1}{2}{\mathrm{O}}_2\to {\mathrm{SO}}_3$ is $-98\mathrm{kJ}$: exothermic, so (C) is false.

$\mathrm{S}\to {\mathrm{SO}}_3$: $-297-98=-395\mathrm{kJ}$, exothermic: (B) true.

${\Delta }_f{H}^{\circ }({\mathrm{SO}}_3)=-395kJ/mol$, not $-98$: (D) false.

Answer: A, B.