Physical Chemistry Lina 2009

8/6/2019 Physical Chemistry Lina 2009

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PHYSICAL CHEMISTRY


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Applied physical chemistry

procedures is used to solve commonenvironmental engineering problems.


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Physical Chemistry - is a combined scienceof physics, chemistry, thermodynamics,electrochemistry and quantum mechanics.It functions to provide molecular levelinterpretation of observed macroscopicphenomena; typically, changes intemperature, pressure, volume and heat

in the liquid solid and gas phase andcorrelates to microscopic atomic andmolecular interactions.


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G asses.Indefinite volume.Indefinite shape.Take the shape and volumeof container.Particles are far apart.Particles move fast

.high Kinetic Energy -particles can separate andmove throughout container..


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Henrys Law

It states that theamount of gas thatdissolves in a liquidis proportional tothe partial pressurethat the gas exertson the surface of the liquid


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Henrys LawCA = K HPA

WhereCA = concentration of A [mol/L] or

[mg/L]KH = Henrys Law constant

[mol/L.atm] or [mg/L.atm]PA = partial pressure of A [atm]


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Air StrippingAir stripping is a common method of removing dissolved gasses from waterand wastewater.G asses commonly removed includeammonia, carbon dioxide and hydrogensulfide.The only gasses with appreciable partialpressure in air are nitrogen andoxygen.


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Air StrippingOther gasses represent only 1% of thetotal pressure.Thus , since the equilibriumconcentration of a dissolved gas isproportional to the partial pressure of thegas on the liquid surface, any gas exceptnitrogen and oxygen can be air strippedto relatively low concentration by bringingit into intimate contact with air.


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Air stripping


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Sample problemAn air-stripping tower is used to removedissolved carbon dioxide from agroundwater supply. If the tower lowersthe level to twice the equilibriumconcentration, what amount of dissolvegas will remain in the water aftertreatment? The partial pressure of carbon

dioxide in the atmosphere is 1 x 10 -3.5 atm.


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IdealG

as Law

Where

PV = nRTWhere:

P = absolute pressure [atm]V = volume [L]n = number of moles [mol]

T = absolute temperature [KR = gas constant [0.0821L.atm/mol.K]


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Sample ProblemAnaerobic microorganisms metabolize

organic matter to carbon dioxide andmethane gases. Estimate the volume of gas produced (at atmospheric pressureand 25 oC) from the anaerobicdecomposition of 1 mol of glucose. Thereaction is

C6H12 0 6 p 3CH 4 + 3CO 2


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D altons Law of Partial Pressure

Dalton's Law

The total pressure of a mixture of gasesis equal to the sum of the partialpressures of the gases in a mixture

Ptotal = PA + PB + PC + ..Pi


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Sample ProblemAnaerobic digester are commonly used inwastewater treatment. The biologicalprocess produces both carbon dioxide

and methane gas. A laboratory workerplans to make a sysnthetic digester gas.There are cu rrently 2L methane gas at1.5 atm and 1 L of carbon dioxide gas at1 atm in the laboratory. If these twosamples are mixed in a 4-L tank, what willbe the partial pressure of individualgasses? What is total pressure?


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It deals with numerical relationshipsbetween reactants and products in

chemical reactions.Stoichiometric analysis can be usedto determine the product yield for agiven amount of reactant converted.

Stoichiometry


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Example of Stochiometric Analysis

Nuetralization of hydrochloric acid withlime

2HCl + Ca(OH)2 CaCl2 + 2H2O

Oxidation of acetic acid to carbon dioxideand water.

CH3COOH + 2O2 2CO2 + 2H2O


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Sample ProblemA trailer truck with a full load of

hydrochloric acid HCl (40,000lbs)crashes into a bridge, spilling the acidinto the stream. How mu ch limeCa(OH) 2 is trequired to neutralize theacid.

The neutralization reaction is2HCl + Ca(OH)2 CaCl2 + 2H2O


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An environmental engineeringapplication of stoichiometry is the

estimation of the amount of oxygen,a known organic chemical willconsume as it is converted to C0 2 andH20.

This is frequently termed asTheoretical Oxygen D emand or ThO D .

Theoretical Oxygen D emand

(ThOD

)


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Theoretical Oxygen D emandIt is simply the amount of oxygen

required to convert the material tocarbon dioxide and water.In situations where the organic

matter contains amine compounds(-NH 2 ), the end produuct of the nitrogen

is ammonia (NH 3 )


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Sample ProblemEthanol or ethyl alcohol is used inbeverages as gasoline additive, andin other industrial applications.Because small amounts of ethanoland sugar are used in the biologicalprocess to produce methanol, both of these compounds end up in thewastewater of methanol plants.


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Sample ProblemCalculate the theoretical oxygen demand for

a wastewater containing:

a) 25 mg/L ethanol CH 3CH 2OHb) 45 mg/L glucose C 6H12 O6c) A mixture of 25 mg/L ethanol and 45

mg/L glucose


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Equilibrium Chemistry

It can be used to analyze avariety of differentaqueous reactions of interest to theenvironmental engineer

or the environmentalengineering student.


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Reactions of environmental significanceincludedetermining the amount of a base to addan acid spill,the amount of acid to neutralize a basicprocess wastewater,the solubility of a metal in a chemical

waste streamand estimating the removal of phosphorusin wastewater treated with lime.


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Mass balance

A mass balance is written statementor equation that describes thedifferent species in which acomponent may exists.


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U NIT OF EXPRESSIONMolarity

Normality


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Adsorption

It is a surface phenomenon in which asolute (soluble material) concentrates orcollects at a surface.

This contrasts with ABSORPTION, whicha substance penetrates the material.


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Ad sorption is a process that occurswhen a gas or liquid solute

accumulates on the surface of a solidor a liquid (adsorbent), forming a filmof molecules or atoms (theadsorbate ).


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Adsorbents Characteristics and G eneralRequirements

They must have high abrasionresistance, high thermal stability andsmall pore diameters, which results in

higher exposed surface area andhence high surface capacity foradsorption.


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The adsorbents must also have adistinct pore structure which enables

fast transport of the gaseous vapors.


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Adsorbents are used usually in theform of spherical pellets, rods,

moldings, or monoliths withhydrodynamic diameters between 0.5and 10 mm.


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Silica gel is a chemically inert,nontoxic, polar and dimensionally

stable (< 400 C) amorphous form of SiO 2 .Zeolites are natural or syntheticcrystalline aluminosilicates whichhave a repeating pore network andrelease water at high temperature.


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Activated carbon is a highly porous,amorphous solid consisting of

microcrystallites with a graphitelattice, usually prepared in smallpellets or a powder. It is non-polarand cheap.


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Activated carbon can be used toremove toxic organics from both

water and air.It is commonly used in aquariumfilters.


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It is used in some potable waterplants to remove organics before or

after chlorination, in industrialwastewater treatment to remove avariety of organics, and occasionallyto remove residual organics following

conventional wastewater treatment.


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It is used in air pollution control toremove organic contaminants from

contaminated air before discharge.

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Physical Chemistry Lina 2009