Final answer:
The boiling point of a substance is a constant temperature at which a liquid changes to a gas, and adding heat at this point does not raise the liquid's temperature but enables vaporization. Only after the liquid has fully evaporated can the temperature of the resulting gas increase with more heat.
Step-by-step explanation:
The boiling point of a substance is not a continuously increasing temperature when heat is added to a boiling liquid. Instead, once a liquid reaches its boiling point, the temperature remains constant while the liquid turns to gas. Heating increases the temperature of the gas phase after all of the liquid has changed to the gas phase. The energy added during boiling does not increase temperature but instead facilitates the transition from the liquid phase to the gas phase, a process known as vaporization.
For example, water has a boiling point of 100°C at 1.00 atm pressure. When water reaches this temperature, the heat added is used to convert the water from a liquid to a gas without raising the temperature of the mixture. The resulting gas, or steam, can then increase in temperature if further heat is applied after the liquid has completely evaporated.
This concept is fundamental to understanding phase changes and is illustrated in a heating curve graph, which summarizes the energetic behavior of water as it transitions through solid, liquid, and gas phases under conditions of constant pressure.