Question

$\Delta S$ for the vaporisation of $900g$ water (in $kJ/K$) is:
[$\Delta H_{vap}-40kJ/mol$]

• A. $(900\times 40)$
• B. $\frac{50\times 40}{373}$
• C. $\frac{900\times 40}{373}$
• D. $\frac{18\times 40}{373}$

Answer 1

The correct option is B $\frac{50\times 40}{373}$

Entropy of vaporisation

$△S_{vap}={}^{}\frac{△H_{vap}}{T_{vap}}$$T_{vap}=Boilingpointof{H}_{2}O$

$=\frac{40}{373}$$permol$${100}^{\circ }c=100+273=373k$

$\therefore for900g=\frac{900}{18}=50molesofwater,$

$△S_{vap}=\frac{50\times 40}{373}kJ/mol$