If you boil water in a pan the boil comes faster if the lid

If you boil water in a pan, the boil comes faster if the lid is left on. WHy? The lid is loose fitting: that is, the pressure in the pan does not increase as it does in a pressure cooker.

Solution

The reason is simple: in order to boil, water must be heated to the boiling point. However, while heat is being introduced at the bottom of the pot, heat is also being lost at the top of the pot, through evaporative cooling and air convection of heat away from the surface of the water.

With the lid on the pot, convective cooling will be substantially curtailed, as cool air will not be able to circulate directly onto the surface of the water to cool it

Additionally, with the lid on the pot, the evaporated water cannot diffuse or convect into the room. It will soon reach vapor pressure equilibrium and begin condensing almost as fast as it evaporates, returning much of the latent heat of evaporation as almost as fast as it is lost (it is not a total recovery, because the pot with lid is not air tight).

So the largest of the cooling effects will be curtailed.