Question

how much ice at 0 degrees C is needed to lower the temperature of 100g

Answer 1

when we add ice at 0 C to water of 100 g, at higher temperature than ice ,

say the temperature of water 50 0C to 20 0C

here the heat lost by ice is heat gain by water as the ice melts become water at 0C and then its temperature will increase from 0 C to 20 0C

ice Q = m*Lf+m*Cw*(DT)

water Q = m*Cw*(DT)

and equating the heat energies

   m*Lf+m*Cw*(DT) = m*Cw*(DT)

substituting the values

   m*334+m*4186(20-0) = 0.1*4186(30)

   m = 0.149 kg
the amount of ice required is 0.149 kg = 149 g