Question

A fog forms over a lake. What two changes of state must occur to produce the fog? Do the water molecules absorb or release energy during these changes of state? What happens to the motion of the water molecules as a result?

Answer 1

Water typically exist in its gaseous state in the atmosphere. Fog contains droplets of liquid water suspended in the air. Thus to produce a fog, vapor in the air would undergo condensation with a state change from gas to liquid.

Intermolecular interactions between water molecules strengthen as the vapor condenses to produce a liquid. The condensation of vapor thus involves a production of energy. With all the extra intermolecular interactions, molecules in the fog would find it more difficult to move around and therefore see a decrease in their motion.