EARTH 222 Lecture 9: Properties of Water

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February 1, 2017
Properties of Water
Three key properties of H2O
Polarity
Due to covalent bonding (sharing of electron) between oxygen and hydrogen
Molecule is positively charged on one end and negatively changed on the other (i.e.
polar)
Hydrogen bonding
Weak bonds (no electron sharing)
Due to attraction of the positive and negative ends of H2O
Present in all three phases in Earth’s temperature range (ice, liquid, and vapor)
Vaporizing water takes the most energy out of all phase changes
Consequences
Water has a very high heat capacity, higher than that of any solid or liquid other than
ammonia
Large quantities of heat required to raise temperature (~4J to raise 1g by 1ºC)
Heat absorbed by H bonds
Moderates coastal temperature
Currents transport large amounts of heat
Ocean water temperatures are relatively stable compared to terrestrial temperatures
Water has a very high latent heat of vaporization, higher than that of any other substance
Massive quantities of heat required to vaporize liquid water
Heat absorbed by H bonds
Key factor in atmospheric heat transport and in hurricane formation
Water has a very high latent heat of fusion, higher than that of any other substance other
than ammonia
When ice forms, most of the energy lost is released to the atmosphere, ice absorbed large
amounts of heat in melting
Ice acts as a thermostat to keep high-latitude water and atmosphere near freezing point
Water undergoes thermal expansion
Pure water has a density maximum at 4ºC
The temperature at which the maximum occurs decreases as salinity increases
Freshwater stays unfrozen under ice in winter in lakes and estuaries
Water is an extremely good solvent, aka “the universal solvent”
Solvent is a liquid that dissolves a solid
Can dissolve more substances than any other liquid
An effective solvent due to polarity
Water dissolves minerals from rocks and transports them to the ocean
Therefore, water is the medium in which the chemical reactions that support life occur
For example, NaCl (table salt) dissolves because Na+ ion is attracted to negative end of
H2O and Cl- is attracted to positive end of H2O
Water attacks and surrounds (or hydrates) ions
Once surrounded by H2O molecules (i.e. hydrated), dissolved ions too far apart to attract
one another
Water is merciless predator of salts, like a piranha
Water’s physical states
The only substance present as a gas, liquid, and solid within the temperature range at the
Earth’s surface
Salinity
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