Question

A fish swimming in water body when taken out from the water body is covered with a film of water of weight 36 g. When it is subjected to cooking at 100 °C, then the internal energy for vaporization in kJ mol-1 is ________. [nearest integer]
[Assume steam to be an ideal gas. Given ΔvapHΘ for water at 373 K and 1 bar is 41.1 kJ mol-1; R = 8.31 J K-1 mol-1]

Answer 1

The correct answer is 38 kJ/mol
$H_2O (l) →H_2O (g)$
$\stackrel{36g}{}$ $\stackrel{36g}{}$
(evaporation)
$n_{H_2O} = \frac{36}{18} = 2$
Δng = 1 – 0 = 1
ΔUvap = ΔHvap – ΔngRT
= 41.1 – (1) × 8.31 × 10–3 × 373
= 41.1 – 3.099
= 38 kJ/mol