When gas is heated, it expands. Imagine a balloon that has some air in it, but not a lot. Now, if the air inside it is heated, the air expands and stretches out the balloon. According to the kinetic molecular theory theory, what is happening to the air molecules that causes the balloon to expand?

A) The molecules are melting.
B) The molecules are moving faster.
C) The molecules are moving slower.
D) The molecules themselves are expanding.

An uncovered pot of water lies out in the sun. which statements correctly describe what happens at the surface of the liquid water? 1. the vapor pressure remains constant regardless of the water temperature. 2. the vapor pressure is produced by water molecules that have evaporated. 3. the vapor pressure increases as the sun heats the water in the pot. 4. evaporation stops once the vapor pressure reaches a certain point. 5. evaporation and condensation both occur on the liquid’s surface.