Final answer:
The phase change during the Heat of Fusion on a heating curve is the transition from solid to liquid, where the substance absorbs energy and the temperature remains constant at the melting point.
Step-by-step explanation:
The phase change that can occur on a heating curve during the Heat of Fusion is the transition from solid to liquid. As heat is added to a substance at a constant rate, its temperature increases until it reaches the melting point. At this stage, temperature remains constant as the substance undergoes a phase change—energy is absorbed but not used for raising the temperature. Instead, the Heat of Fusion is absorbed to break the molecular bonds in the solid, allowing it to become a liquid. Latent heat is the term for the heat absorbed or released when a substance changes phase without changing temperature.
The heating curve of water is a typical example, where ice absorbs heat at a constant rate until it reaches 0°C, the melting point. During melting, the temperature stays at 0°C while the ice absorbs additional energy equivalent to the enthalpy of fusion, which for water is 334 kJ/kg, until all the ice has melted into liquid water. Once melted, the liquid water then starts to increase in temperature again as more heat is added.