GEG 3102 Lecture Notes - Lecture 1: Supercritical Fluid, Paleoclimatology, Cryosphere
17 Oct 2016
School
Department
Course
Professor
1 - Water
September 9, 2016
Introduction to water:
- Water is found in the: magnetosphere (blocks ionizing radiation), atmosphere (gasses
around the planet), biosphere (life on planet), geosphere (solid part of the earth
[lithosphere]), cryosphere (ice and sphere), anthroposphere ([transformed by] humans),
hydrosphere (water)
- The covalent bonds that hold oxygen and hydrogen together are very strong & hard to
break apart (intramolecular bond)
- Hydrogen bonds hold water molecules together, and are constantly breaking & reforming
• Much weaker than covalent bonds, but stronger than other intermolecular bonds
• Gives water its fluidity
- Isotopes:
• Def: A variation of a chemical element which has a different number of neutrons
- Isotopes have the same charge, but different weights
• Oxygen: 16O, 17O (rare) and 18O are all stable
• Hydrogen: 1H (very common) and 2H
• Some molecules of are heavier and some are lighter (based on combination of
isotopes)
- Lighter molecules require less energy to evaporate, so evaporate
preferentially
• Stable isotopes are used to study: paleoclimate reconstructions, global water
cycles, and basin hydrology
- Physical properties of water:
• Under normal pressure water can be found in 3 states: solid, liquid & gaseous
- Under very high pressures and temperatures it can be a supercritical fluid
• Density: liquid = 999.97 kg/m3, solid = 917 kg/m3
- Highest density is at ~ 4 °C (density change is not linear)
• High specific heat
- The amount of heat required (per unit mass) to raise the temperature by
one degree Celsius
• State is dependent on temperature and pressure
- The boiling point of water decreases with pressure (cooking at altitude)
- Supercritical fluid: 374.4 °C and 217 atm (cannot be found naturally)
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• Phase changes:
- Amount of energy added remains constant, but the heat accumulates over
time, raising the amount of energy added
- Mixture of water and ice remains at 0 °C even as more energy is added
• It takes a lot of energy to change the phase, energy in the system
goes toward the phase change, not heating the water (latent heat)
- Latent heat is the energy that is stored in the water when it changes phases
• Vs. sensible heat (heat that can be felt)
• Fusion (solid → liquid): 80 kcal
• Vaporisation (liquid → gas): 540 kcal
• Sublimation (solid → gas): 740 kcal
- Chemical properties:
• Solvent:
- Can react as an acid (H+) or as a base (OH-)
- Dissolves more substances than any other liquid (inc. gasses [O2])
• Provides a rich environment for life
- Water is a necessary condition for life on Earth
Classifications of water
- Salinity: Dissolved salt content
• Total quantity of solids after all organics and carbonates have been oxidized
• Water is classified based on the salinity in parts per thousand (ppt or %o)
- Brine: 50+ %o
- Saline: 30-50 %o
- Brackish: 0.5-30 %o
- Freshwater: 0-0.5 %o (can still have some salt, just not a lot)
- Salinity includes all salt ions, not just sodium chloride
• Sea water is ~55% chloride (Also includes sodium, sulfate,
magnesium, calcium, potassium and other constituents)
- Listed in descending order of importance
• Salinity is highly variable across the oceans
- PSU (practical salinity unit) = ppt
- Polar regions tend to have lower salinity than the tropics
- Rivers that flow into the ocean bring small amount of salts with them
(even fresh water), once in the ocean the water evaporates but leaves the
salt behind increasing the salinity (to a point [saturation])
- Map of annual mean sea surface salinity
- Location: Its location in relation to land surface
• Atmospheric, surface, soil or ground water
- Soil water is above the water table (unsaturated zone) and groundwater is
below the water table (saturated zone)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Water is found in the: magnetosphere (blocks ionizing radiation), atmosphere (gasses around the planet), biosphere (life on planet), geosphere (solid part of the earth. [lithosphere]), cryosphere (ice and sphere), anthroposphere ([transformed by] humans), hydrosphere (water) The covalent bonds that hold oxygen and hydrogen together are very strong & hard to break apart (intramolecular bond) Hydrogen bonds hold water molecules together, and are constantly breaking & reforming: much weaker than covalent bonds, but stronger than other intermolecular bonds, gives water its fluidity. Isotopes: def: a variation of a chemical element which has a different number of neutrons. Isotopes have the same charge, but different weights: oxygen: 16o, 17o (rare) and 18o are all stable, hydrogen: 1h (very common) and 2h, some molecules of are heavier and some are lighter (based on combination of isotopes) Lighter molecules require less energy to evaporate, so evaporate preferentially: stable isotopes are used to study: paleoclimate reconstructions, global water cycles, and basin hydrology.
