Question

Which of the following reaction(s) can be spontaneous?

• A. $H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(l\right)$; $△$ H = -285.7 kJ/mol
• B. $H_{2}O\left(l\right)\to H_{2}O\left(g\right)$; $△$ H = +44 kJ/mol
• C. $N{H}_{4}Cl\left(s\right)\to N{H}_4^{\oplus }\left(aq\right)+C{l}^{\ominus }\left(aq\right)$; $△$ H = +15.1 kJ/mol
• D. All of these

Answer 1

The correct option is D

All of these

A process that can progress by itself without requiring any external source of energy at a given set of conditions and when there is decrease in system's free energy is called a spontaneous process.
Sign of $\Delta G$ determines whether a reaction is spontaneous or not, according to equation
$\Delta G=\Delta H-T\Delta S$
when $\Delta G$ = -ive , reaction is spontaneous
$\Delta G$ = +ive, reaction is non spontaneous.
$\Delta G$ = 0, reaction is at equilibrium

From the above equation it is clear that the reactions can be spontaneous irrespective of the sign that $\Delta H$
takes as sign and magnitude of $T\Delta S$ also matters.

Therefore, all of the given reactions can be spontaneous.