#1) Reaction: [6H + (aq) + H 2 O (l) + Ca 3 Al 2 Si 3 O 12(s) <--> Al 2 Si 2 O 5
ID: 997221 • Letter: #
Question
#1) Reaction: [6H+(aq) + H2O(l) + Ca3Al2Si3O12(s) <--> Al2Si2O5(OH)4(s) + 3Ca2+(aq) + H4SiO4(aq)]
#3) Reaction: [Al2Si2O5(OH)4(s) + 6H+(aq) <--> 2Al3+(aq) + 2H4SiO4(aq) + H2O(l)]
- Although this reaction is correctly balanced; I am not sure if this is the reaction to use, or if I should just use the first reaction from question 1.
- I am confused on the difference between Ksp and the equilibrium constant K, please explain the difference in detail and how to solve them separately given the information in the picture.
- Can you use the equation {log(K)= -[?G/(2.303RT)]} calculating for K in the same way to calculate Ksp?
- What is the difference between IAP and Ksp? I am confused on calculating the saturation index using IAP and Ksp, because they always seem to be the same value. Please explain in detail.
#4) {log(K1/K2) = (-?Hrº/R) [(1/T1)-(1/T2)]}
INTRODUCTION TO GEOCHEMISTRY (GCH 3303) HOMEWORK #9, SPRING 2016 Due: April 14, 2014 The chemical weathering of grossular garnet (CasAl,S 012 ) is a common reaction in 1. At standard conditions, which mineral is more stable when in contact with a ground water soils and forms the clay mineral kaolinite (Al SigOs(OH)s ) comprising: mol I,'' G/ (kJ mol") pH 7 (H) H O H4SiO4 Car Grossular garnet Ca AlbS,012 Kaolinite Al-SizOs(OH)4 s -237.129 10-1307.7 10 553.58 -6281.359 3799.7 Hint: a balanced reaction is needed. 2. Calculate the equilibrium constant for the reaction at standard conditions 3. The reaction is not in equilibrium at standard conditions. Is the groundwater supersaturated or undersaturated with respect to kaolinite? Hint: saturation indices and ion activity products (IAP) Using the van't Hoff equation, calculate the equilibrium constant for the reaction between gross conditions is t,'--268.48 kJ ular garnet and kaolinite at 250 . The enthalpy for the reaction at standardExplanation / Answer
(1) At standard condition, the mineral salt which has the greatest -ve free energy is most stable. Thus among the two minerals grossular garnet, Ca3Al2Si3O12 is more stable.
(2) When considering salts, Ksp means K equilibrium, so we may use the same equation.
Under standard condition,
equilibrium constant Ksp,
dGo = -RTlnKsp
-6281359 = -8.314 x 298 lnKsp
Ksp = infinity [very high solubility]
(3) IAP = (actual concentration)
Ksp = (equilibrium concentration)
IAP = (Ca2+)^3.(H4SiO4) = (10^-4)^3.(10^-3.5) = 3.16 x 10^-16
IAP < Ksp, so the solution would be undersaturated.
(4) Van't hoff equation,
ln(k2/k1) = dH/R[1/T1 - 1/T2]
T1 = 298 K
T2 = 250 + 273 = 523 K
k1 = can be ignored since it is too high
R = gas constant
dH = -268.48 kJ
we get,
ln(k2) = -268480/8.314 [1/298 - 1/523]
So the required equilibrium constant becomes,
k2 = 5.67 x 10^-21
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