Natural Water Systems

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Natural Water Systems
Atmosphere
dnA
Phase Transfer
Water
dnA
dnA
Flux in
Flux Out
Chemical Reaction A?B
dnA
dnA
Phase Transfer
Solid and liquid phases
2
Concentration Scales
Invariant with P,T
Varies with P,T
Solids and Gases
3
Concentration Scales
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Components
Components
Gas
CaO - CO2 - H2O CaCO3 - CO2 - H2O
Water
Phase Rule
F C - P 2 F 3 - 3 2
Calcite
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Components
Species
Ca2 CO2 aq, CO2 gas H2CO3, HCO3-, CO3 H,
OH- H2Oliq, H2Ogas CaCO3 calcite
Gas
Water
Phase Rule
Calcite
F S - R - P 2
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Component Species
Fixed by mass balance equations
or by charge balance equation
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Derived Species
Fixed by mass action expression (equilibrium
constant)
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Enthalpy
Heat content at constant pressure
Heat capacity
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Enthalpy
0 0 -68.315 ?fH ?rH -68.315
kcal/mole
Exothermic
-118.22 -60.27 -49.0 ?fH ?rH
-60.27 (-49.0) - (-118.22) 8.95
kcal/mole
Endothermic
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Entropy
Second Law
Third Law
S of a pure crystalline solid 0 at 0 K
Dissolved ions
ST for H 0
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Gibbs Function
Equilibrium condition ?G 0 Spontaneity
condition ?G lt 0
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Equilibrium Constant
Consider the reaction
?rG 0 at equilibrium
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Equilibrium Constant
At equilibrium
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Equilibrium constants
?fG -1797.36 -552.8 -744.0 -237.14
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Conventional Standard States
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Equilibrium Constant
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Summation of Ks
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Saturation Index
where
Substitute definition of ?Gr
Collect terms and rearrange
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Saturation Index
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Saturation Index
Data
Reaction Direction
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Temperature Shift
Integrate from T1 to T2 (assuming H independent
of T)
Vant Hoff Equation
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Temperature change
When ?Cp ?0 then ?Hr is not constant
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Temperature change
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Vant Hoff Equation
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Water Activity
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Gases
Ideal gas
Partial Pressure in Dry Air
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Gases
Gas solubility
Dissolved O2
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Solids
1
Raoults Law Real behavior Henrys Law
?i
0
0
1
Xi
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Pressure Change
If ?V is independent of Pressure then
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P T Effects on Kw