What is the change in entropy when water is vaporized at 100°C. Latent heat of vaporization of water may be taken as 2238 kJ/kg.

Correct option is C

​$$\begin{aligned}&\textbf{Given:} \\&\bullet\ \text{Latent heat of vaporization } L = 2238\, \text{kJ/kg} \\&\bullet\ \text{Temperature } T = 100^\circ C = 373\, \text{K} \\[1em]&\textbf{Sol.} \\&\text{The \textbf{change in entropy} during a \textit{phase change at constant temperature} is given by:} \\&\Delta S = \frac{Q_{\text{rev}}}{T} \\[1em]&\text{Where:} \\&Q_{\text{rev}} = L = 2238\, \text{kJ/kg} = 2238000\, \text{J/kg} \\&T = 373\, \text{K} \\[1em]&\text{Now, compute:} \\&\Delta S = \frac{2238000}{373} \approx 6001.6\, \text{J/kg} \cdot \text{K} = 6.002\, \text{kJ/kg} \cdot \text{K}\end{aligned}$$​​