Why does water steam before its boiling point?

Answer 1

As the temperature increases and the water approaches its boiling condition, some molecules attain enough kinetic energy to reach velocities that allow them to momentarily escape from the liquid into the space above the surface, before falling back into the liquid.

Further heating causes greater excitation and the number of molecules with enough energy to leave the liquid increases. As the water is heated to its boiling point, bubbles of steam form within it and rise to break through the surface.

Considering the molecular structure of liquids and vapours, it is logical that the density of steam is much less than that of water, because the steam molecules are further apart from one another. The space immediately above the water surface thus becomes filled with less dense steam molecules.

When the number of molecules leaving the liquid surface is more than those re-entering, the water freely evaporates. At this point it has reached boiling point or its saturation temperature, as it is saturated with heat energy.

Basically steam is invisible. What your seeing is not steam. Its the point at which the warm air (from the kettle) meets the cold air.

Answer 2

Water can start steaming below its boiling point due to a process called evaporation. When the temperature of the water is below boiling point, some of the water molecules at the surface gain enough kinetic energy to overcome intermolecular forces and escape as vapor, creating steam.