Water: A Natural Wonder
pointing arrows (condensation and freezing) represent processes that release or give off energy.
In the energy diagrams in the text, these arrows are shown in blue.
Many common substances, including gasoline, rubbing alcohol, and cooking oil are liquid at
STP, that is, at one atmosphere (now one bar) pressure and 0
C (273 K).
Many substances, including the components of the Earth’s atmosphere, nitrogen (N
), argon (Ar), carbon dioxide (CO
), and water vapor, are gases at STP.
When water freezes the volume of the solid is greater than the volume of the liquid. If a closed
glass bottle initially filled entirely with water is kept outside at a temperature below the freezing
point of water, the water will freeze, expand, and break the bottle. Note that this is what is
shown in these pictures from
, Chapter 1, Section 1.1, page 3, in which a plastic
bottle filled with water ruptures when the water freezes:
If one boils a solution of NaCl
and water, the water will evaporate (vaporize) and the
salt will be left behind due to the fact that water has a much lower boiling point than table salt,
which is a solid at 100
A laboratory distillation apparatus for the separation of a sodium chloride solution is shown
here. Boiling the solution evaporates the water, which is condensed in the inner tube of the
condenser, and runs down to be collected in the receiving flask. After all the water has boiled
remains in the boiling flask.