Question

As water heats in a pot on a stove, it might produce some mist above its surface right before the water begins to roll. What is happening?

Answer 1

When a liquid is heated, the molecules gain kinetic energy. As the liquid begins to boil they have enough energy to break the intermolecular attractions between their neighbors. This happens first at the surface before the volume below has enough energy to boil. Thus you see high energy water molecules escaping from the surface as mist.

Answer 2

As the liquid water gains energy in the form of temperature, the kinetic energy of the particles increase, this causes that some bonds "break".

Now, when this happens in the top of the water (where the pressure is smaller) some of the particles can "escape" the water, and form this "mist" that you can see, this is because actually the temperature of change of phase depends on the pressure, so in the top of the water there are less pressure keeping the particles in place, and they need smaller temperature to change of phase.