Question

1. How much energy (in kilojoules) is released when 16.4 g of steam at 116.5 ∘C is condensed to give liquid water at 60.5 ∘C? The heat of vaporization of liquid water is 40.67 kJ/mol, and the molar heat capacity is 75.3 J/(K⋅mol) for the liquid and 33.6 J/(K⋅mol) for the vapor.

2.What is the entropy of fusion, ΔSfusion [in J/(K⋅mol)] for sodium? The necessary data are the following:
mp = 97.8 ∘C,bp = 883 ∘C, ΔHvap = 89.6kJ/mol, and ΔHfusion = 2.64kJ/mol.

Answer 1

Problem1:

step1: No of moles of H₂O =16.4/18=0.811moles

step2: Heat released by cooling steam to 100⁰C=0.911x33.6x16.5=505.05j/mole=0.505kj

step3: Heat released by condensation at 100 degree c=0911x40.67=37.05kj

step4; heat released on cooling from 100degree c to 60.5⁰C=0.911x75.3x39.5=2709j/mole=2.7kj/mole

So, released energy released=0.505+37.05+2.7=40.2kj

problem2:

∆S°(fus) = ∆H°(fus)/T(mp)

∆S°(fus) = (2640 J/mol)/(370.8 K) = 7.12 J mol⁻¹ K⁻¹