Final answer:
In a closed pan on a range, water undergoes an endothermic process where it absorbs heat, leading to boiling. Convection currents are formed, and if not for the lid, evaporation would occur. The paddle wheel assists in even heat distribution.
Step-by-step explanation:
When water is being heated in a closed pan on top of a range while being stirred by a paddle wheel, several processes are occurring simultaneously. First and foremost, this is an example of an endothermic process because heat is being added to the system to raise the temperature of the water, ultimately leading to the water boiling. As the water heats up, convection currents are formed due to the fact that hotter water expands, becomes less dense, and rises, while cooler water moves to take its place at the bottom of the pan. If the pan was not closed, evaporation would occur, with water molecules transitioning from the liquid to gas phase below the boiling point; however, in a closed container, evaporation is counterbalanced by condensation, where water vapor condenses back into the liquid form.
The paddle wheel introduces another element—mechanical work which can enhance the heat distribution throughout the water more evenly and can aid the process of boiling by preventing hot water from only rising in one place.