Question

When you breathe out, there is water vapor in your breath. When you breathe on a cold window in the winter, the window gets tiny droplets of moisture on it or “fogs up.” What happens to the molecules of water vapor as they get near the cold window?

Answer 1

The water molecules in your breath are the gas water vapor. They slow down as they transfer some of their energy to the cold window. The attractions between the slower-moving water vapor molecules bring them together to form tiny droplets of liquid water.