remains constant
This plot of temperature shows what happens to a 75 g sample of ice initially at 1 atm and 23C as heat is added at a constant rate: AB: heating solid ice; BC: melting ice; CD: heating liquid water; D E: vaporizing water; EF: heating steam. Thus the temperature of a system does not change during a phase change. In this example, as long as even a tiny amount of ice is present, the temperature of the system remains at 0C during the melting process, and as long as even a small amount of liquid water is present, the temperature of the system remains at 100C during the boiling process. The rate at which heat is added does not affect the temperature of the ice/water or water/steam mixture because the added heat is being used exclusively to overcome the attractive forces that hold the more condensed phase together. Many cooks think that food will cook faster if the heat is turned up higher so that the water boils more rapidly. Instead, the pot of water will boil to dryness sooner, but the temperature of the water does not depend on how vigorously it boils.