Question

Ice at `0^@C` is added to 200 g of water initially at `70^@C` in a vacuum flask. When 50 g of ice has been added and has all melted the temperature of the flask and contents is `40^@C`. When a further 80 g of ice has been added and has all melted the temperature of the whole becomes `10^@C`. Find the latent heat of fusion of ice.
A. `80 cal//gm`
B. `90 cal//gm`
C. `70 cal//gm`
D. `540 cal//gm`

Answer 1

Correct Answer - B
According to principle of calorimetry
`ML_(f) + MS Delta theta = (mS Delta theta)_(water) + (mS Delta theta)_(flask)`
`5L_(f)=400+3w`…(i), here `w = (ms)_(flask)`
Now the system contains `(200+50) gm` of water at `40^@C`, so when further `80 gm` of ice is added
`8 L_(f) = 670 + 3w` ....(ii)
from (i) & (ii) we get `L_(f)`.