Final answer:
At the boiling point, heat energy goes into vaporization, converting liquid to gas without raising temperature. This isothermal process continues until all liquid transitions to gas, after which further heating raises the gas's temperature. The system's entropy increases as the molecules move more freely.
Step-by-step explanation:
When the temperature of a liquid reaches its boiling point, the heat energy added to the system does not increase the temperature further. Instead, this energy is used to convert the liquid into a gas, a process known as vaporization. This phase transition occurs at a specific temperature and is an isothermal process.
During boiling, the temperature of the system remains constant as heat is absorbed to overcome the attractive forces between the molecules, facilitating the change from liquid to gas. After all the liquid has evaporated, any additional heat increases the temperature of the gas.
The entropy of the system increases when the water is heated to its boiling point. This is because the disorder in the system increases as the water molecules begin to move more freely in the gas phase, compared to their restricted movement in the liquid phase.