Which of the following statements is true as a block of ice melts?

• A. The melting process is exothermic.
• B. The pressure decreases as the ice melts at constant temperature.
• C. The temperature of the mixture increases steadily as the ice melts.
• D. The temperature of the ice-water mixture remains constant until all the ice has melted.

Answer: (D)

Verified step by step guidance

1. Understand the phase change process: When ice melts, it undergoes a phase transition from solid to liquid at a constant temperature (0°C at 1 atm pressure). This is a key concept in thermodynamics related to phase changes.
2. Recall that during melting, the system absorbs heat energy without a change in temperature. This energy is called the latent heat of fusion, which is used to break the hydrogen bonds in ice rather than increasing temperature.
3. Analyze the nature of the melting process: Melting is an endothermic process, meaning the system absorbs heat from the surroundings. Therefore, the statement that melting is exothermic is false.
4. Consider pressure changes: At constant temperature and pressure, the pressure does not necessarily decrease as ice melts. In fact, melting typically occurs at a specific pressure and temperature equilibrium, so pressure remains constant or controlled externally.
5. Summarize the temperature behavior: Since the temperature remains constant during the melting process until all ice has melted, the correct statement is that the temperature of the ice-water mixture remains constant during melting.