Question

Calculate the entropy change $\left[J/\right(mol.K\left)\right]$ of the given reaction. The molar entropies $\left[J/\right(K.mol\left)\right]$ are given in brackets after each substance :

$2PbS\left(s\right)\left[91.2\right]+3O_2\left(g\right)\left[205.1\right]\to 2PbO\left(s\right)\left[66.5\right]+2S{O}_2\left(g\right)\left[248.2\right]$

• A. $-113.5$
• B. $-168.3$
• C. $+72.5$
• D. $-149.2$

Answer 1

Answer: (B)

$-168.3$

$\Delta S=$ (Sum of entropy of product)-(Sum of entropy of reactant)

$\Delta S=\left\{\right(2\times 66.5)+(2\times 248.2\left)\right\}-\left\{\right(2\times 91.2)+(3\times 205.1\left)\right\}$

$\Delta S=-168.3\frac{J}{molK}$

$\therefore$ Option B is correct