Matter often changes.  When enough heat is added to a liquid, it will begin to boil and turn into a gas.  The bubbles are water vapor, and as more heat is added, the bubbles become larger and larger. The boiling point of a liquid is the temperature at which the liquid begins to vaporize.  The added heat gives the molecules in the liquid more kinetic energy.  Vaporization is the change from a liquid state to a gaseous state.  Vaporization can be used to describe both boiling and evaporation.  Evaporation is vaporization that occurs only at the surface of a liquid.  It can occur at temperatures below the liquid’s boiling point.  For example, if you leave a cup of water unattended on the counter, the water will eventually evaporate.

When something melts, it changes from a solid state to a liquid state.  The melting point is the temperature at which a solid melts.  When something freezes, it changes from a liquid state to a solid state.  The freezing point is the temperature at which a liquid freezes. Condensation occurs when there is a change from a gaseous state to a liquid state.  The condensation point is the temperature at which gas condenses.

Review:

1. What is boiling point?
2. When does condensation occur?
3. Explain evaporation.