What occurs when ice reaches 0°C and starts to melt?

• A. Temperature increases rapidly
• B. Heat is removed from the system
• C. Heat is added while temperature remains constant
• D. The phase change occurs without heat transfer

Answer: (C)

When ice reaches 0°C and begins to melt, heat is added to the system while the temperature remains constant. This process is known as a phase change, specifically from solid (ice) to liquid (water).

At 0°C, the ice requires additional energy, termed latent heat of fusion, to facilitate the transition from solid to liquid. This energy does not increase the temperature; rather, it is used to break the bonds between the ice molecules, enabling them to move more freely as a liquid. During this phase change, the temperature is maintained at 0°C until all the ice has melted. This concept is critical in thermodynamics and illustrates how substances can absorb or release heat during phase transitions without a change in temperature.

Other potential options, such as an increase in temperature or heat removal from the system, do not accurately describe the behavior of ice melting at this crucial point, where it specially requires energy to change phase rather than increase in temperature or lose heat.