HOMEWORK 3 ANSWER KEY
GEO 131 Spring 2007
The special properties of water (universal solvent, high boiling point) are related to its low
- it is related to its asymmetrical shape which creates a charge imbalance (i.e., a
polar charge distribution). The hydrogen end is positively charged and the oxygen end is
negatively charged. This charge imbalance enables water molecules to pull apart other
molecules, thereby making water a universal solvent. The charge imbalance also causes
the water molecules to be strongly attracted to one another, thereby raising the boiling
point of water.
Water can dissolve almost anything because of the shape of the water molecules and the
charge distribution on them.
- The positive charge on one end and the negative charge on the other end of the V-
shaped water molecule creates an electrical attraction for the molecules near to them, and
can thereby pull molecules apart.
If ice sufficiently compressed, it will melt- even at temperatures below freezing.
- Because ice must expand in order to develop the ordered crystalline structure
characteristic of the frozen state, compression destroys this structure and results in
On a cold winter day, an unfrozen lake will lose heat energy faster than a lake with a frozen
- Ice acts like a layer of insulation because it slows the rate at which heat energy
can escape from the underlying water.
The charge distribution on water molecules is relevant to dissolving things, but not to the
phase changes that water undergoes.
- the charge distribution results in an attraction between water molecules - the
positive end of one water molecule attracts the negative end of another. As a result, this
increases the amount of energy required for phase changes. If it weren’t for this fact,
water would not serve as the “fuel for storms.”
Many substances on earth undergo phase changes within the temperature range that occurs
naturally on earth.
- only water does this - which is one of the reasons why it is so special.
It is also
why the hydrologic cycle occurs.
If water did not possess this property, life as we know
it would be impossible on earth.
The reason temperature changes result in phase changes is because the change in temperature
affects the speed of the molecules.
- by affecting the speed of the molecules, a change in temperature affects the ability
of the chemical bonds to hold molecules together. For example, as the temperature
increases, the speed of the molecules increases, thereby reducing the effectiveness of the
bonds. This leads to a change from either a solid to a liquid, or a liquid to a gas,
depending upon the original state of the matter and the amount of temperature increase.
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