Question

Calculate the change of entropy ${\Delta }_r{S}_m^{\circ }$ at 298 K for the reaction in which urea is formed from $N{H}_3$ and $C{O}_2$. The standard entropy of $N{H}_{2}CON{H}_2$ is 174.0 $J{K}^{-1}mo{l}^{-1}$. For $N{H}_3$, $C{O}_2$ and $H_{2}O$ it is 192.3, 213 and 69.9$J{K}^{-1}$

• A.
• B. 354.4 JK
• C. 453.4
• D. 273 JK

Answer 1

The correct option is A

${\Delta }_r{S}_m^{\circ }=\sum V_p{S}^{\circ }\left(products\right)-\sum V_p{S}^{\circ }\left(reactants\right)=\left[\right(174.0+69.9)-(2\times 192.3+213\left)\right]J{K}^{-1}mo{l}^{-1}=(243.9-598.8)J{K}^{-1}mo{l}^{-1}=-354.4J{K}^{-1}$