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Properties of Water
Ocean motions governed by fundamental physical laws of conservation of mass, momentum and energy
Water’s truly unique property as related to Earth System Science:
At standard pressure, water changes from a liquid to a solid at 0° C (32°F) and from a liquid to a gas at 100°C (212°F). Only substance that can exist in all three phases within the Earth’s range of temperatures.
Other properties of water (additional properties in Table 7.2):
- great heat storage ability
- little internal friction
- dissolves solids and gases readily (“universal solvent”)
- changes phase in atmosphere and in ocean
- solid form floats
- transparent to some wavelengths of light, nearly opaque to others
- high surface tension
Geography 104 - “Physical Geography of the World’s Oceans”
Question:Why does water behave the way it does?
Answer:Water’s properties are due to its unique molecular structure.
Chemistry 101
- protons, electrons and (usually) neutrons form atoms- atoms, building blocks of matter, bond to form molecules- hydrogen (H) and oxygen (O) bond to form water (H2O)
Chemical bonding involves electrons- ionic bond involves transfer of electrons- covalent bond involves sharing of electrons
water molecule
covalent bonds between oxygen and two hydrogen atoms
oxygen attracts electrons more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom.
hydrogen bonds
Electrical attraction between molecules
freshwater density vs. temperature
surface tension
surface tension
Physical implications of surface tension: - capillary waves - viscosity (thickness or internal friction)- molecular diffusion
day-night temperature differences on earth’s surface
Energy is necessary to drive ocean processes.
Forms of energy important to oceanographers (Table 7.1) - solar energy- thermal energy- kinetic energy- potential energy- chemical energy
How does water store and exchange thermal energy or heat?- heat capacity - relationship between heat and temperature- temperature - measure of average kinetic energy of molecules- heat - spontaneous transfer of energy from a high temperature system to a lower temperature system
specific heat - (Cp) amount of heat necessary to change the temperature of a unit mass by 1 °C
James Joule (1818 – 1889)heat gain equivalent to potential energy loss
joule (J) – energy from a force of 1 Newton moving through distance of 1 meter
specific heat values
water = Cp(T,P) ~4180 J kg-1 °C-1
seawater = Cp(T,S,P) ~4000 J kg-1 °C-1
silicon (sand) = ~710 J kg-1 °C-1
concrete = ~752 J kg-1 °C-1
air = ~1000 J kg-1 °C-1
ice = ~2050 J kg-1 °C-1
sea breeze – as land warms to temperature greater than ocean during day
land breeze – as land cools to temperature lower than ocean during night
specific heat differences between ocean and land influences local weather
water structure and phase transitions
Heat must be added/removed to alter hydrogen bonds and change state of water. This heat not expressed in a change of temperature.
2. /
energy and phase transitions
Figure 7-11 in text; another error
3. /
0. Energy to heat 1 gm ice by 1 °C = 2.05 J/g
Readings for next time (thermodynamics of water):
Read first part of Chapter 7 (pgs 113 – 122)