1 gm ice at -40 deg Celsius is placed in a container havng 1gm water at 1 deg Celsius.  Find equlilbrium temperature

heat reqd to raise the temp of ice to 0 degree C = 1*0.5*40 = 20 cal

heat reqd to conver ice at 0 degree C to water at 0 degree C = mL = 1*80 = 80 cal

so total = 100 cal

But to conver 1 gm of water at 1 degree C to 1 gm of ice at 0 degree C , heat reqd = 1+ 80 = 81

so temp of mixture = 0 degree C