(a) One kilogram of water at 273 K is brought into contact with a heat reservoir at 373 K. When the water has reached 373 K, what is the entropy change of the water, of the heat reservoir, and of the universe?
(b) If the water had been heated from 273 to 373 K by first bringing it into contact with a reservoir at 323 K and then with a reservoir at 373 K, what would have been the entropy change of the universe?
(c) Explain how the water might be heated from 273 to 373 K with almost no change of entropy of the universe.