2 폐기물실험실

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1 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 where R 1 and R 2 = reactants, P 1 and P 2 = products, and b, c, m, and n = stoichiometric coefficients. 1 폐기물실험실

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3 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

4 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

5 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 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

6 (Reading Assignment, 2-3 Organic Chemistry p59-62) 6 폐기물실험실

7 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

8 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

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

9 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

10 [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

11 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 = where K w = equilibrium or dissolution constant for water (dependent on temperature) 11 폐기물실험실

12 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

13 + 2- [H ] [CO 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

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15 3.5 Inorganic Impurities Ions in water Table Most prevalent ions in natural waters, along with typical molar concentrations Ion Seawater (M) River water (M) Na x 10-3 Mg x 10-3 Ca x 10-3 K x 10-3 Cl x 10-3 SO 4 2- HCO x x 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] Ionic strength 1 2 I = å (Ci z i ) 2 i 15 폐기물실험실

16 where I = ionic strength - Ionic strength of water significantly affect the activities of ionic species in water 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 ( mg/l as CaCO 3 ), very Hard (> 300 mg/l as CaCO 3 ) Alkalinity - the capacity of water to neutralize acids 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

17 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

18 Microbial Fuel Cell 4.2 Combustion 18 폐기물실험실

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

슬라이드 제목 없음

슬라이드 제목 없음 물리화학 1 문제풀이 130403 김대형교수님 Chapter 1 Exercise (#1) A sample of 255 mg of neon occupies 3.00 dm 3 at 122K. Use the perfect gas law to calculate the pressure of the gas. Solution 1) The perfect gas law p