Here's a breakdown:
1. Energy Input: When you heat a liquid, you're adding energy to its molecules. This energy increases their kinetic energy, causing them to move faster and vibrate more vigorously.
2. Overcoming Intermolecular Forces: As the temperature rises, the molecules gain enough energy to overcome the attractive forces (like hydrogen bonding, dipole-dipole interactions, or London dispersion forces) that hold them together in the liquid state.
3. Phase Change: At the boiling point, the molecules have enough energy to completely break free from their liquid neighbors and escape into the vapor phase. This phase change requires a significant amount of energy, called the heat of vaporization.
4. Constant Temperature: The energy you continue to input is used to break more bonds and vaporize more molecules, rather than increasing the kinetic energy of the remaining liquid molecules. Therefore, the temperature remains constant until all the liquid has been converted into vapor.
In essence, the energy supplied at the boiling point is entirely consumed in the process of overcoming intermolecular forces and changing the state of matter, rather than increasing the temperature. This is why the temperature remains constant during boiling, even though heat is still being added to the system.
