Question

The standard entropies of $N_2\left(g\right), H_2\left(g\right)$ and $NH_3\left(g\right)$ are $191.5, 130.5, 192.6 \,JK^{-1}\, mol^{-1}$. The value of $\Delta S^{\circ}$ during the formation of $1$ mole of ammonia is

• A. $- 98.9 \,JK^{-1}\, mol^{-1}$
• B. $-9.78\, JK^{-1}\, mol^{-1}$
• C. $+ 129.4\, JK^{-1} \,mol^{-1}$
• D. Zero

Answer 1

Answer: (A)

$\frac{1}{2}N_{2}+\frac{3}{2} H_{2}\to NH_{3}$
$\Delta S^{\circ}=192.6-\left(\frac{1}{2}\times191.5+\frac{3}{2}\times130.5\right)$
$=192.6-\left(95.75+195.75\right)$
$=192.6-291.5=-98.9 JK^{-1} mol^{-1}$