Boiling water is an endothermic process. This means that during the boiling of water, heat is absorbed from the surrounding environment.
When water reaches its boiling point (100 degrees Celsius at sea level), the heat energy provided by the heat source is used to overcome the intermolecular forces between water molecules. This energy allows the molecules to move apart and transition from the liquid phase to the gaseous phase (steam).
As the water absorbs this heat, it requires energy to convert the liquid into vapor. Thus, throughout the boiling process, heat is continuously taken in, making it endothermic. In summary, boiling water involves absorbing heat energy, transforming the state from liquid to gas, which characterizes it as an endothermic reaction.