Question

For which process will $\Delta H^\circ $ and $\Delta G^\circ $ are expected to be most similar?

• A. $2Al\left(\right.s\left.\right)+Fe_{2}O_{3}\left(\right.s\left.\right) \rightarrow 2Fe\left(\right.s\left.\right)+Al_{2}O_{3}\left(\right.s\left.\right)$
• B. $2Na\left(\right.s\left.\right)+2H_{2}O\left(\right.l\left.\right) \rightarrow 2NaOH\left(\right.aq.\left.\right)+H_{2}\left(\right.g\left.\right)$
• C. $2NO_{2}\left(\right.g\left.\right) \rightarrow N_{2}O_{4}\left(\right.g\left.\right)$
• D. $2H_{2}\left(\right.g\left.\right)+O_{2}\left(\right.g\left.\right) \rightarrow 2H_{2}O\left(\right.g\left.\right)$

Answer 1

Answer: (A)

$2Al\left(\right.s\left.\right)+Fe_{2}O_{3}\left(\right.s\left.\right) \rightarrow 2Fe\left(\right.s\left.\right)+Al_{2}O_{3}\left(\right.s\left.\right)$

As in this reaction all reactants and products are in solid states so in this reaction $\Delta S^\circ \approx 0$ hence $\Delta G^\circ \approx \Delta H^\circ $ .

$\Delta G=\Delta H-T\Delta S\approx \Delta H-0\approx \Delta H$