If water boils at 100°C, and boiling is the process of turning liquid into gas, why are bathrooms full of steam when showering at only 40°C?

Question

If water boils at 100°C, and boiling is the process of turning liquid into gas, why are bathrooms full of steam when showering at only 40°C?

In: Chemistry

Answer 1

ELI5: All molecules in water are always moving chaotically, bumping into each other, changing direction, and so on. You can roughly think that the temperature of water is the speed of an average water molecule. (Strictly speaking, temperature is the average kinetic energy, which is the mass of a molecule times the speed squared.)

Imagine you are a molecule on the surface of the water. You can try to leave it (evaporate), but there are two forces that prevent this. First, other water molecules try to stop you and keep you inside. This is called intermolecular forces. Second, molecules of air also try to push you back. That’s why only strong and fast molecules (with high kinetic energy) can overcome both forces and actually leave the water (evaporate).

If only the fast molecules leave the water and the slow ones stay, the average speed of the remaining molecules gets lower, which means the temperature drops. This is why water cools down when it evaporates.

Now to the boiling point. The boiling point is when the average Joe of water molecules is fast enough (has enough kinetic energy) to overcome both forces and leave the water.