Question

How much heat energy is require to raise 5 mol of solid water at -25 C to liquid water at 35 C (Heat of fusion=6.01 kJ/mol, molar heat capacity of ice=37.6 J/mol*C, molar heat capacity of water=75.2 J/mol*C?

Answer 1

For converting solid water at -25 deg.c to 35 deg.c, the following heat needs to be supplied

1. Sensible heat needs to be supplied to ice for convering it from -25 deg.c to 0 deg.c = moles of ice * specific heat of ice* Temperature difference= 5*37.6 j/mol.c {0-(-25}= 4700 joules

2. Ice has to be melted at constant temperature of 0 deg.c to convert it into liqud at 0 deg.c and this comes from latent heat of fusion and total latent heat to be supplied = moles of ice* latent heat ( Kj/mol)= 3*6.01Kj= 18.03 KJ= 18.03*1000 J= 18030 joules

3. Liquid water needs to be heated from 0 to deg.c to 35 deg,c by suplying sensible heat= moles * specific heat of liquid ( j/mol.deg.c) * temperature difference= 3*75.2*(35-0)=7877 joules

the total heat to be supplied= Sensible heat of ice ( from - 25 deg.c to 0 deg.c) (1)+ latent heat ( from 0 deg.c ice to liquid water at 0 deg.c) (2)+ sensible hea of liquid ( from 0 deg.c to 35 deg.c) (3)=4700+ 18030+ 7877= 30607joules=30.607 KJ ( 1000 J= 1Kj)