Answer:
When water reaches its boiling point, which is typically 100°C at standard atmospheric pressure, the temperature of the water does not increase further despite continuous heating. Instead, the energy supplied to the water is used to facilitate the phase change from liquid to gas (water to water vapor). This phase change occurs at a constant temperature and the energy supplied goes into the latent heat of vaporization of the water.
Explanation:
The scenario you described involves heating water from 20°C to 80°C. In this case, the water temperature rises, but it does not reach the boiling point. However, if we were to continue heating the water beyond 80°C up to 100°C, the water would eventually start to boil and then the temperature would remain at 100°C until all the water has evaporated.
The specific heat capacity of water, which you've provided as 4.18 J/g°C, is only relevant when the water is not undergoing a phase change. It indicates the amount of heat needed to raise the temperature of 1 gram of water by 1°C. Once boiling begins, the heat energy goes into changing the phase of water rather than raising its temperature.