What is the net change in entropy of the system from the time of mixing until the moment the ice completely melts? The heat of fusion of ice is .
Note that since the amount of ice is relatively small, the temperature of the water remains nearly constant throughout the process. Note also that the ice starts out at the melting point, and you are asked about the change in entropy by the time it just melts. In other words, you can assume that the temperature of the "ice water" remains constant as well.
In a well-insulated calorimeter, 1.0 of water at 20 is mixed with 1.0 of ice at 0.