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Water Exam Review for h2o.docx

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Earth Sciences
John Maclachlan

20140422Water Exam Review NotesWater BasicsIntroductionWater is NOT an element It is a compound that consists of two hydrogen atoms covalently bonded to one oxygen In general covalent bonds are 1050 times stronger than hydrogen bonds Furthermore water can form hydrogen bonds that facilitate movement of water through systems This property also allows water to act as a very good solvent Physical and Chemical Properties of WaterTheproperties of water includephysical1Density Water is denser than ice Ice remains at the top of a lake during winter 2Expansion Water expands when it cools3Specific heat The amount of energy it takes to raise 1 kg of water by 1 degree4Phase change Energy is required to change liquid to a gas5Greenhouse gas Invisible water vapour reflects reflecting solar radiation such that it remains This results in warming of the Earth 6Surface tension Water is more attracted to itself than other water molecules This in a spherical shape if there was no gravitational force because there is a stronger interaction insideDetergent will reduce surface tension between water molecules This is the basis of functioning in plant systems via capillary action ie movement of water superior and into a narrow opening The meniscus in tubes occur because water wants to retain its spherical shape If the adhesive force liquidsolid exceeds cohesive force liquidliquid then the liquid can wet the solid Otherwise it will appear as droplets on the surface of solid The chemical properties of water include1Solvation Dissolves many substances spontaneously 2Ionic substances Hydrogen has a partial positive whilst oxygen has a partial negative These will respectively breakup the sodium and chlorine lattice structuresalt3Polar substances These substances have partial charges on the atoms which will interact with partial charges on water for solvationsugar4Non polar substances do not dissolve in water such as oil etc5Small size The small size of water molecules relative to other elements allows many water molecules to surround a signal atom This assists in solvation 20140422Water BasicsHuman brains consist of 95 water Loss of water results in a variety of adverse symptoms 2 loss results in feeling of thirst 5 loss results in a headache 15 loss results in death In the beginning water was used for agricultural propagation Furthermore this resulted in development of a society As society developed the uses of water diversified The severe water scarcity OECD is a value that determines the threshold of water scarcity of an area 3 This is less than 500 mper person per year Currently 28 countries are below this threshold indicating that there is a severe water scarcity There are many estimates of conditions in India However regardless of the estimate all agree that India will experience water scarcity in 2050 Potable water is defined as water suitable for human consumption without health risks Water reclamation is treatment of wastewater such that it becomes usable Grey water is water used by use in washing machines tubs showers etc Planned indirect potable water use is extracting the water using it then returning it naturally upstream of the treatment water plant Unplanned indirect potable water use is the extraction of water then entry of water back into natural system after it has been used without deliberation Direct potable water use is extraction but then direct insertion of water back into the water supply Indirect water use inserts reclaimed water into secondary sources that drain into the water source where drinking water is abstracted Direct water use would involve putting it directly back into the water source Water UseWater can be used in three ways1InStream The water is NOT taken out rather it is used as is eg Hydro dams2OffStream The water IS taken out used and returned to source 3Consumptive Water Use The water IS taken out and NOT returned Overall in the world water is used MOST for agricultural practices The countries that do not have access to water will become exporter of goods These countries will export these goods in return for water This is referred to as the external water footprint There are five methods to increase water efficiency focus efforts in areas with low yields improve soil fertility in arid and semiarid areas trade to manage water efficiency reduce evaporation and use biotechnology Coal and nuclear plants use a lot of water Nuclear plants have to shut down if the temperature of water exceeds a certain threshold Water CycleMost of the water is stored in the sea Most of the freshwater is stored in glaciers then groundwater then lakes then soil moisture and then wetlands Domestic use of water is minimal The thicker the arrow the more the water moves Air above a water body is warmer This increases the capacity of the air to hold onto water As air moves over land it will cool down This decreases the capacity of air to hold onto water resulting in precipitation 20140422Four things can happen to water as it falls to the ground1Interception This is precipitation caught by obstructions prior to it reaching the ground This is dependent upon vegetation type land use seasons intensity and magnitude of precipitation and initial conditions 2Storage It is stored as snow or ice3Runoff This is a gravity driven process where the water will move on ground surface towards a stream This is dependent upon slope angle and substrate materialIn general there will ONLY be runoff iff the precipitation rate is greater than the infiltration rate The infiltration rate is defined as the amount of water that infiltrates or passes into the ground 4Evapotranspiration This is the combination of evaporation and transpiration Evaporation is dependent upon temperature initial conditions and wind Transpiration is dependent upon type of vegetation season wind andinitial conditionsDeciduous trees have a higher evapotranspiration rate Furthermore windy summer days also have higher evapotranspiration The ClausiusClapeyron CC relation states that water vapour pressure increases as temperature increases Furthermore undersaturated air can become supersaturated with water with a slight decrease in temperature or cooling Saturated water vapour pressure is the pressure exerted by water molecules in air that is saturated with water vapour In generalhas a higher saturated water vapour pressure than wateroice below 0C Furthermore there are many uncertainties with the global water cycle For instance researchers have an extremely wide range of the amount of annual precipitation Basically we do not know how much it rains Albedo represents the percentage of solar radiation that is reflected back into space This is an important concept because the smaller the albedo the warmer the climate will be Furthermore there is a snowice
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