2 폐기물실험실

II. Basic Water Chemistry 1. Governing Concepts - Stoichiometry ( 화학양론식 ): - Chemical Equilibrium ( 화학적평형 ): - Reaction Kinetics ( 반응동역학 ): 1.1 Stoichiometry b R + c R m P + n P 1 2 1 2 where R 1 and R 2 = reactants, P 1 and P 2 = products, and b, c, m, and n = stoichiometric coefficients. 1 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim1

2 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim2

1.2 Chemical Equilibrium - The underlying theory for chemical equilibrium is based on thermodynamics. A + B Û C + D At equilibrium, the rate of forward reaction is identical to it of reverse reaction. The rate of forward reaction is expected to proportional to the rate of collisions between A and B. It means that the rate of forward reaction is directly proportional to the concentrations of A and B. R = k [A] [B] f f where R f = rate of the forward reaction; k f = rate constant (vary with temperature); and [A], and [B] = concentrations of A and B. R = k [C] [D] r r where R r = rate of the reverse reaction; k r = rate constant (vary with temperature); and [C], and [D] = concentrations of C and D. At equilibrium, R = R f r k f [A] [B] = k [C] [D] r [C] [D] k = f = K [A] [B] k r 3 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim3

where K = equilibrium constant of the reaction (constant at a fixed temperature) a A + b B Û c C + d D c d [C] [D] [A] a [B] b = K 1.3 Reaction Kinetics - When a system is at equilibrium? - How much time is needed for a system to reach equilibrium? - What can we say about systems that are not at equilibrium? A + B 1 ¾¾ C 4 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim4

R 1 æ d[a] ö æ d[b] ö æ d[c] ö = - ç = - ç = ç è dt ø è dt ø è dt ø 1 1 1 where a, b, c, and d = stoichiometric coefficients; A and B = reactants; C = product; and 1 = arbitrary symbol to identify the reaction. g a A + b B ¾¾ c C + d D R g 1 æ d[a] ö 1 æ d[b] ö 1 æ d[c] ö 1 æ d[d] ö = - = - = = a ç dt b ç dt c ç dt d ç dt è ø è ø è ø è ø a Rg = kg [A] [B] g g g g b where k g = rate constant (a function of temperature, or a function of pressure for gaseous reactions); and a and b = empirical coefficients. For an elementary reaction (On the other hand, a and b must be determined experimentally) a Rg = kg [A] [B] b Zero-order reaction: R = k g First-order reaction: Rg = kg [A] or Rg = kg [B] g Second-order reaction: R 2 g = kg [A], R 2 g = kg [B], or R = k [A] [B] g g 5 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim5

(Reading Assignment, 2-3 Organic Chemistry p59-62) 6 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim6

2. Phase Changes and Partitioning 2.1 Vapor Pressure Definition: At equilibrium condition between a species in the vapor phase and a flat surface of the pure liquid of the specimen, 0 0 P i = K vp or P i (T) = K vp (T) where P i o = equilibrium partial pressure of species i (dependent on temperature); K vp = an equilibrium constant (i.e., vapor pressure, dependent on temperature). Relative Humidity: the amount of water vapor in air PH 2O RH = 100% O P (T) H2O where RH = relative humidity; P H2O = actual partial pressure of water vapor; and P 0 H2O (T) = saturation vapor pressure at given temperature. For a mixture of single volatile liquid and nonvolatile impurities, the dilution of a liquid with nonvolatile impurities reduces the vapor pressure of the liquid because nonvolatile molecules occupy a portion of the surface, reducing the area from which evaporation takes place. Thus, higher temperature is needed than the pure liquid boils (Raoult s law). 0 0 P (T) = X P (T) i,mix i i 7 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim7

where X i = the mole fraction of the volatile component in the mixture. 2.2 Dissolution of Species in Water Partitioning between the gas phase and water: Henry s law C w = KH,g P g or P g = Hg Cw where C w = equilibrium concentration in the aqueous phase; K H,g and H g = Henry s law constant; and P g = equilibrium partial pressure in the gas phase. 8 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim8

Solubility of Nonaqueous-Phase Liquids NAPL (nonaqueous-phase liquid): Under equilibrium conditions, the quantity of the NAPL that dissolves in water depends on the species and the temperature, but not on the volume of the NAPL. C i (T) = K ws (T) where C i = equilibrium concentration of NAPL compound i dissolved in water; and K ws = water solubility for the compound. Dissolution and Precipitation of Solids A B x y «xa +yb ( : dissolution, and : precipitation) 9 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim9

[A] x y [B] = K sp(t) where K sp = solubility product ( 용해도적 ) 2.3 Sorption - Adsorption: - Absorption: Sometimes it is not possible to distinguish between adsorption and absorption. Then, 10 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim10

the term sorption is used. Sorption Isotherms Linear: q e = Kads Ce Freundlich: Langmuir: q = K C 1/n e f e q = q e max b Ce 1 + b C e where q e = equilibrium mass of sorbed molecules per mass of sorbent; and C e = equilibrium concentration of contaminant molecules in a fluid. Isotherm means uniform temperature. Partitioning varies with temperature. 3. Acid-Base Reactions - Since acid-base reactions are generally very fast, ph predictions are almost always based on the assumption of equilibrium. 3.1 Acid-Base Reactions and the Hydrogen Ion - Hydrogen ions do not exit as free H + species in aqueous solution. H 3 O + is highly favored. The resulting ion may have one or more additional water molecules loosely bound to it. - Acid and Base (donate or lose hydrogen ion or electron) 3.2 ph of Pure Water H 2 O H + + OH - ' K = + - [H ] [OH ] [H O] 2 K [H 2 O] = [H+][OH-] = K w = 10-14 where K w = equilibrium or dissolution constant for water (dependent on temperature) 11 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim11

3.3 Strong and Weak Acids HA H + + A - K = A + - [H ] [A ] [HA] where K A = acid dissociation constant pk A are less than 1, strong acid 3.4 Carbonate-Bicarbonate System CO 2 (g) CO 2 (aq) H 2 CO 3 (aq) HCO - 3 (aq) CO 2-3 (aq) CaCO 3 (s) carbon dioxide gas dissolved carbon dioxide carbonic acid (a diprotic, weak acid) bicarbonate ion carbonate ion calcium carbonate (limestone) CO 2 (g) vs. CO 2 (aq) [CO 2 (aq)] = K H P CO2 CO 2 (aq) vs. H 2 CO 3 (aq) CO 2 (aq) + H 2 O H 2 CO 3 [H2CO 3] = K -2.8 A = 10 2 [CO (aq)] For engineering purposes we combine CO 2 (aq) and H 2 CO 3 (aq) into one variable, H 2 CO * 3 because it is difficult to experimentally differentiate between CO 2 (aq) and H 2 CO 3. [H 2 CO * 3 ] = [CO 2 (aq)] + [H 2 CO 3 (aq)] = [CO 2 (aq)] (1 + K A ) [CO 2 (aq)] H 2 CO 3 * vs. HCO 3 - (aq) H 2 CO 3 * H + + HCO 3 - (aq) HCO 3 - (aq) vs. CO 3 2- (aq) + - [H ] [HCO 3 ] -6.3 * = K 1 = 10 [H2CO 3 ] HCO 3 - (aq) H + + CO 3 2- (aq) 12 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim12

+ 2- [H ] [CO 3 ] -10.3 - = K 2 = 10 [HCO 3 ] CO 3 2- (aq) vs. CaCO 3 (s) CaCO 3 (s) Ca 2+ + CO 3 2- (aq) K sp = [Ca 2+ ] [ CO 3 2- (aq)] C carbonate = [H 2 CO 3 * ] + [HCO 3 - (aq)] + [CO 3 2- (aq)] Distribution of aqueous carbonate species as a function of ph - Figure 2-10 (p. 69), and 2-11 (p.70) 13 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim13

14 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim14

3.5 Inorganic Impurities 3.5.1 Ions in water Table Most prevalent ions in natural waters, along with typical molar concentrations Ion Seawater (M) River water (M) Na + 0.47 0.23 x 10-3 Mg 2+ 0.053 0.15 x 10-3 Ca 2+ 0.010 0.33 x 10-3 K + 0.010 0.03 x 10-3 Cl - 0.55 0.16 x 10-3 SO 4 2- HCO 3-0.028 0.07 x 10-3 0.0024 0.86 x 10-3 3.5.2 Electroneutrality å z C = 0 i i where z i = charge per molecule on the i th ion; and C i = the molar concentration of the i th ionic species [M]. 3.5.3 Ionic strength 1 2 I = å (Ci z i ) 2 i 15 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim15

where I = ionic strength - Ionic strength of water significantly affect the activities of ionic species in water. 3.5.4 Hardness - the sum of normalities of all multivalent cations (i.e., charge of +2 or greater) - Hardness is often expressed in terms of the equivalent mass concentration of calcium carbonate (CaCO 3 ). For example, a hardness of 1 meq/l is the same as a hardness of 50 mg/l as CaCO 3. - Soft (< 75 mg/l as CaCO 3 ), Hard (150-300 mg/l as CaCO 3 ), very Hard (> 300 mg/l as CaCO 3 ). 3.5.5 Alkalinity - the capacity of water to neutralize acids - - 2- + 3 3 A = [OH ] + [HCO ] + 2[CO ] - [H ] where A = alkalinity 4. Oxidation-Reduction Reactions - Acid-base reactions: transfer of protons - Oxidation-reduction reactions (Redox reactions): 4.1 Corrosion 16 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim16

A galvanic cell may occur in a water supply system when two dissimilar metals, such as iron and copper pipe, are connected. In this case, the iron will corrode. 17 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim17

Microbial Fuel Cell 4.2 Combustion 18 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim18

4.3 Atmospheric oxidation processes Thermal reactions vs. Photolytic reactions 4. 4 Microbial Reactions Photosynthetic production of biomass +4-2 0 0 hv CO 2 + H2 O ¾¾ {C H2O} + O2 Aerobic Respiration 0 0 +4-2 {C H O} + O CO + H O Nitrogen Fixation 2 2 2 2 0 0 +4-3 + 2 2 2 2 4 3{C H O} + 2 N + 3H O + 4H 3CO + 4 N H + Nitrification -3 0 +5-2 -2 + - + N H 4 + 2O 2 N O 3 + 2H + H2 O Nitrate Reduction (or Denitrification) 0 +5 +4 0 - + 2 3 2 2 2 5{C H O} + 4 N O + 4H 5CO + 7H O + 2 N Sulfate Reduction 0 +6 +4-2 + 2-2 4 2 2 2 2{C H O} + 2H + S O 2CO + 2H O + 2H S Methane Formation 0 +4-4 2{C H O} CO + C H 2 2 4 19 폐기물실험실 http://plaza.snu.ac.kr/~jaeykim19