Question

A 500 g bar of ice is initially at -25 °C. Calculate the amount of energy required to vapourize 25% of the substance at 100 °C.

Answer 1

Mass of ice, $m=500\space g$

Initial temperature of ice, $T_i$ = $-25\degree C$

Final temperature, $T_f=100\degree C$

Mass of ice to be vapourized, $m'=0.25\times500=125\space g$

We know specific heat of ice is 0.5 cal/gK,

specific heat of water=1cal/gK

Also latent heat of fusion= 80 cal/g

latent heat of vaporization=540 cal/g

Ice(248K)→ice(273K)→water(273K)→water(373K)→steam(373K)

Total heat absorbed,

$(125\times25+80\times125+125\times100+125\times540)$

$=93,125\space cal$