Answer
What is the change in entropy of 250 g of steam at 100 degrees C when it is condensed to water at 100 degrees C?
Condensatio takes away heat energy from the water. Therefore, we know that the change in entropy will be negative. The heat transfer is just the mass of the steam times its latent heat of vaporization.
DS = Q/T = mLvap/T = (0.25 kg)(2.25 kg)(22.6x105 J/kg)/(273 + 100) K = -1.5x105 J/K