Properties of Properties of WaterWater

Three major properties of waterThree major properties of water

ThermalThermal-- density propertiesdensity propertiesHigh specific heatHigh specific heatLiquidLiquid-- solid characteristicssolid characteristics

Molecular Structure Molecular Structure -- Basis of Basis of PropertiesProperties

At equilibrium At equilibrium -- HH22O molecule forms O molecule forms isosceles triangle with obtuse angle of isosceles triangle with obtuse angle of 104.5104.5°° at oxygen atomat oxygen atomContinual state of vibrationContinual state of vibrationSeveral ionized statesSeveral ionized states

HH33OO++

OHOH--

HH44OO++++

OO----

Molecular Structure Molecular Structure -- Basis of Basis of PropertiesProperties

Weak Weak coulombiccoulombic characteristics of characteristics of hydrogen bonded to weakly hydrogen bonded to weakly electronegative oxygenelectronegative oxygenBoth ionized and covalent states occurBoth ionized and covalent states occurWater is almost the only known compound Water is almost the only known compound that exhibits these characteristicsthat exhibits these characteristics

Density RelationshipsDensity Relationships

Specific gravity Specific gravity -- Ratio of the mass of a Ratio of the mass of a substance to the mass of an equal volume substance to the mass of an equal volume of a reference substance (usually water)of a reference substance (usually water)Specific gravity of pure ice at 0Specific gravity of pure ice at 0°°C is C is 0.916800.91680Specific gravity of water at 0Specific gravity of water at 0°°C is 0.99987C is 0.99987From 0From 0°°C, specific gravity of water C, specific gravity of water increases to a maximum of 1.0000 at increases to a maximum of 1.0000 at 3.983.98°°CC

Figure 2-3, page 12

Important !!!!!Important !!!!!

Density RelationshipsDensity Relationships

Density difference per degree lowering Density difference per degree lowering -- the the difference in density between water at a given difference in density between water at a given temperature and water at a temperature 1temperature and water at a temperature 1°°C C lowerlower

Physical work is required to mix fluids of Physical work is required to mix fluids of different densitydifferent density

Work is proportional to difference in densityWork is proportional to difference in density

Density RelationshipsDensity Relationships

Work required to mix water Work required to mix water between 29between 29°°C and 30C and 30°°C is C is

40 times greater40 times greaterthan work required to mix water than work required to mix water between 4between 4°°C and 5C and 5°°C (24C (24°°C and C and 2525°°C C -- 30 times)30 times)

Effect of salinity on densityEffect of salinity on densityDensity increases as concentration of Density increases as concentration of dissolved salts (salinity) increasesdissolved salts (salinity) increasesIncrease is approximately linearIncrease is approximately linearSalinity of lakes is generally in the range Salinity of lakes is generally in the range of 0.01 of 0.01 -- 1.0 g/l1.0 g/lRange is most commonly 0.01 Range is most commonly 0.01 -- 0.5 g/l0.5 g/lSaline lakes can exceed 60 g/lSaline lakes can exceed 60 g/lSalinity of seawater is 35 g/lSalinity of seawater is 35 g/l

Effect of salinity on densityEffect of salinity on densityTemperature of maximum density Temperature of maximum density decreases as salinity increasesdecreases as salinity increases -- rate rate of 0.2of 0.2°°C/g/lC/g/lMaximum density of seawater is at Maximum density of seawater is at --3.523.52°°CC

Effect of PressureEffect of Pressure

Pressure can compress water and lower Pressure can compress water and lower temperature of maximum densitytemperature of maximum densityPressure increases by 1 atmosphere per Pressure increases by 1 atmosphere per 10 m of depth10 m of depthTemperature of maximum density Temperature of maximum density decreases 0.1decreases 0.1°°C/100 m of depthC/100 m of depth

Structure of IceStructure of IceEach molecule is HEach molecule is H--bonded to nearest bonded to nearest four neighborsfour neighborsEvery oxygen atom is at the center of a Every oxygen atom is at the center of a tetrahedron formed by four oxygen tetrahedron formed by four oxygen atomsatomsOO--H bonds are directed toward H bonds are directed toward electrons of adjacent oxygen moleculeelectrons of adjacent oxygen molecule

Structure of IceStructure of IceIts lone pairs of electrons are directed Its lone pairs of electrons are directed toward Otoward O--H bonds of adjacent H bonds of adjacent moleculesmoleculesResults in open lattice with both Results in open lattice with both perpendicular and parallel voidsperpendicular and parallel voidsVoids allow ice to float on waterVoids allow ice to float on water

Structure of IceStructure of Ice

Ice molecules vibrate (translational Ice molecules vibrate (translational and reorientation movement) at a rate and reorientation movement) at a rate of 10of 1066 movements/sec at 0movements/sec at 0°°CCWater at 0Water at 0°°C vibrates at 10C vibrates at 101212

movements/secmovements/secRate of vibration increases as Rate of vibration increases as temperature increases and results in temperature increases and results in decreasing viscositydecreasing viscosity

Structure of IceStructure of Ice

As water melts, HAs water melts, H--bonds are disrupted bonds are disrupted and water fills the voids and density and water fills the voids and density increasesincreases

Above 3.98Above 3.98°°C, vibrations increase and C, vibrations increase and the distance between bonds increases the distance between bonds increases and density decreasesand density decreases

Water is a liquid crystalWater is a liquid crystalHydrogen bonds create lattice even in liquid Hydrogen bonds create lattice even in liquid phasephaseWater freezes at 0Water freezes at 0°°C and boils at 100C and boils at 100°°CCOn the basis of van On the basis of van derder WaalsWaals forces alone, forces alone, water would be expected to freeze at water would be expected to freeze at --100100°°C C and boil at and boil at --8080°°CCWater and mercury are the only inorganic Water and mercury are the only inorganic compounds that exist as liquids at the compounds that exist as liquids at the temperature and pressure found at the earth's temperature and pressure found at the earth's surfacesurface

Specific HeatSpecific Heat

Specific heat is the amount of heat in Specific heat is the amount of heat in calories that is required to raise the calories that is required to raise the temperature 1temperature 1°°C of a unit mass (usually C of a unit mass (usually 1 gram) of a substance1 gram) of a substanceSpecific heat of water is 1.0 Specific heat of water is 1.0 -- very highvery high

Specific HeatSpecific Heat

Few substances have a higher specific Few substances have a higher specific heatheat

Liquid ammonia Liquid ammonia -- 1.231.23Liquid hydrogen Liquid hydrogen -- 3.43.4

Most substances have much lower Most substances have much lower specific heatsspecific heats

Rocks Rocks -- 0.20.2

Latent HeatsLatent Heats

Water also has a high latent heat of Water also has a high latent heat of evaporation evaporation -- heat energy required to heat energy required to evaporate a unit mass of liquid at a evaporate a unit mass of liquid at a constant temperatureconstant temperature

Latent heat of evaporation Latent heat of evaporation -- 540 cal/g540 cal/gLatent heat of melting Latent heat of melting -- 79.72 cal/g79.72 cal/gLatent heat of sublimation Latent heat of sublimation -- 679 cal/g679 cal/g

Latent HeatsLatent Heats

Water also has a high latent heat of Water also has a high latent heat of evaporation evaporation --

Heat energy required to evaporate a unit Heat energy required to evaporate a unit mass of liquid at a constant temperaturemass of liquid at a constant temperature

Latent heat of evaporation Latent heat of evaporation -- 540 cal/g540 cal/g

Latent HeatsLatent Heats

Latent heat of evaporation Latent heat of evaporation -- 540 cal/g540 cal/g

Latent heat of melting Latent heat of melting -- 79.72 cal/g79.72 cal/g

Latent heat of sublimation Latent heat of sublimation -- 679 cal/g679 cal/g

Specific Heat and Latent HeatsSpecific Heat and Latent HeatsThese heat characteristics are a function of the These heat characteristics are a function of the heat energy required to disrupt hydrogen bondingheat energy required to disrupt hydrogen bonding

Environmental ConsequencesEnvironmental Consequences

HeatHeat--requiring and heatrequiring and heat--retaining retaining properties of water provide a much more properties of water provide a much more stable environment in aquatic systems stable environment in aquatic systems than in terrestrial systemsthan in terrestrial systemsFluctuations in temperature are gradualFluctuations in temperature are gradualSeasonal and diurnal extremes are small Seasonal and diurnal extremes are small compared to terrestrial systemscompared to terrestrial systems

Environmental ConsequencesEnvironmental Consequences

Climate is strongly affected by bodies of Climate is strongly affected by bodies of waterwaterAreas near major bodies of water have Areas near major bodies of water have mild winters with higher mild winters with higher preciptitationpreciptitation rates rates and moist, cool summers.and moist, cool summers.Steaming lakes Steaming lakes -- water vapor from water vapor from evaporation condenses in cooler overlying evaporation condenses in cooler overlying air massesair masses

Environmental ConsequencesEnvironmental Consequences

Latent heat of melting is high Latent heat of melting is high -- water water warms slowly and large energy losses are warms slowly and large energy losses are required to form ice coverrequired to form ice coverLatent heat of evaporation is high Latent heat of evaporation is high -- much much heat is expended in evaporation therefore heat is expended in evaporation therefore water warms slowlywater warms slowly

ViscosityViscosity--Density Density RelationshipsRelationships

Viscosity is the tendency of a solution to Viscosity is the tendency of a solution to resist flowresist flowViscosity increases as density increasesViscosity increases as density increasesDensity of water is 775 times greater that Density of water is 775 times greater that air at STPair at STPViscosity changes as temperature Viscosity changes as temperature changeschanges

ViscosityViscosity--Density Density RelationshipsRelationships

Viscosity is related to buoyancyViscosity is related to buoyancyAquatic organisms require less supportive Aquatic organisms require less supportive tissuetissueSinking rates are regulated by buoyancy Sinking rates are regulated by buoyancy and therefore viscosityand therefore viscosity

Surface TensionSurface TensionBonding properties are disrupted at the Bonding properties are disrupted at the airair--water interfacewater interfaceMolecular attractions are directed Molecular attractions are directed inward toward liquid phaseinward toward liquid phaseSurface tension of water is higher than Surface tension of water is higher than that for any other liquid except mercurythat for any other liquid except mercury

Surface TensionSurface TensionSurface tension decreases with Surface tension decreases with increasing temperatureincreasing temperatureSurface tension increases slightly with Surface tension increases slightly with dissolved saltsdissolved saltsSurface tension is greatly reduced by Surface tension is greatly reduced by the addition of organic compoundsthe addition of organic compounds