A calorimeter of water equivalent 15g contains 165g of water at 25∘C. Steam at 100∘C is passed through the water for some time. The temperature is increased to 30∘C and the mass of the calorimeter and its contents is increased by 1.5 g. Calculate the latent heat of vaporization of water. Heat capacity of water is 1 cal/g∘C
Let L be the specific latent heat of vaporization of water.
The mass of the steam condensed is 1.5g.
Heat lost in condensation of steam is Q1=(1.5g)L
The condensed water cools from 100∘C to 30∘C.
Heat lost in this process is = Q2=(1.5g)(1 cal/g∘C)(70∘C)=105 cal
Heat supplied to the calorimeter and to the cold water = Q3=(15g+165g)(1 cal/g∘C)(5∘C)=900 cal
If no heat is lost to the surrounding,
Q1+Q2 = Q3
(1.5)L+105=900
L=530 cal/g