Q. 50 mL of water takes 5 min to evaporate from a vessel on a heater connected to an electric source which delivers 400 W. The enthalpy of vaporisation of water is
A) 40.3 kJ per mol
B) 43.2 kJ per mol
C) 16.7 kJ per mol
D) 180.4 kJ per mol
Explanation
(b)
Work done in 1 $s = 400$ J
Hence, work in 5 min (300 s)
$= 400 \times 300 = 120$ kJ
$\mathrm{\Delta}H_{vap.}^{o} = \frac{120\ kJ}{50/18}$ = 43.2 kJ/mol
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.