What fraction of water supercooled down to the temperature `t = -20 ^@C` under standard pressure turns into ice when the system passes into the equilibrium state ? At what temperature of the supercooled water does it turn into ice completely ?

Explanation

When a portion of supercool water turns into ice some heat is liberated, which should heat it upto ice point. Neglecting the variation of specific heat of water, the fraction of water turning inot ice is clearly
`f = (c|t|)/(q) = 0.25`
where `c` = specific heat of water and `q` ~~ latent heat of fusion of ice, clealy `f = 1` at `t = - 80^@C`.