Question

Identify the substance in each of the following pairs of samples that has the higher entropy?
(A) ${Br}_2\left(l\right)$ or ${Br}_2\left(g\right)$ (B) $C_2{H}_6\left(g\right)$ or $C_3{H}_8\left(g\right)$
(C) $MgO\left(s\right)$ or $NaCl\left(s\right)$ (D) $KOH\left(s\right)$ or $KOH\left(aq\right)$

Answer 1

$\left(A\right)$ $B{r}_2\left(l\right)$ or $B{r}_2\left(g\right)$

Gases have more randomness than liquid due to inter molecular forces.

$\Delta S_{B{r}_2\left(g\right)}>\Delta S_{B{r}_2\left(l\right)}$

$\left(B\right)$ $C_2{H}_6\left(g\right)$ or $C_3{H}_8\left(g\right)$

$\Delta S_{C_3{H}_8}>\Delta S_{C_2{H}_6}$

Larger molecules have more ways to randomly distributes energy at a given temperature.

$\left(C\right)$ $MgO\left(s\right)$ or $NaCl\left(s\right)$

$\Delta S_{NaCl}>\Delta S\left(MgO\right)$

$NaCl$ as it will easily break into ions and will be stable as ions. $MgO$ will break down ions but oxygen tends to be unstable and react with itself to produce $O_2$.

$\left(D\right)$ $KOH\left(s\right)$ or $KOH\left(aq\right)$

$\Delta S_{KOH\left(aq\right)}>\Delta S_{KOH}\left(s\right)$

In aqueous solution $KOH$ will break into $K^{+}$ and $O{H}^{-}$ and randomness will increase while $KOH\left(s\right)$ will have rigid crystal structure.