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Geochemistry > Aqueous Geochemistry > Flashcards

Aqueous Geochemistry Flashcards

1
Q

Physical geologic processes

A

With or without participation of geofluids

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2
Q

Chemical geologic processes

A

Participated by geofluids

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3
Q

Composition of geofluids

A

Variable amounts of components derived from dissolution of solid materials and gases

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4
Q

Dissolved species

A

Materials dissolved in water may be in the forms of molecules or ions

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5
Q

What reaction is always in the background?

A

H2O = H+ + OH-

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6
Q

Dissolved components

A

May be in the form of different species.
The total amount of the dissolved component is the sum of all the dissolved species

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7
Q

Avogadro’s number

A

1 mole of a substance = 6.02 x 10^23 that substance

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8
Q

Molality (m) is = to what?

A

moles / kg water

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9
Q

Molarity (M) is = to what?

A

moles / liter solution

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10
Q

What are the two types of geochemical reactions?

A

1) fluid-fluid reactions
2) fluid-rock reactions

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11
Q

Open system

A
  • Fluid flows through the fluid-rock system
  • Composition is controlled externally
  • Fluid-rock ratio = high
  • Chem eq = not reached
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12
Q

Closed system

A
  • Fluid is stagnant in the fluid-rock system
  • Composition is controlled internally
  • Fluid-rock ratio = low
  • Chem eq = reached
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13
Q

True or False: The geochemical reaction equation is NOT unique for a given pair of reactant & product

A

True

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14
Q

Chemical reaction equilibrium

A

Forward reaction rate = Reverse reaction rate

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15
Q

Le Chatelier’s Principle

A

If equilibrium is disturbed, reaction will proceed in the direction that will counteract the disturbance

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16
Q

Difference between concentration and activity

A

Concentration: (A)
Activity: [A]

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17
Q

Law of mass action equation

A

K =[C]^c [D]^d / [A]^a [B]^b

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18
Q

How is equilibrium constant K determined?

A
  • Experiment at specific P-T-X conditions
  • Calculations from thermodynamic database
19
Q

Congruent dissolution

A

The dissolution of one mineral is not accompanied by precipitation of another mineral

20
Q

Incongruent dissolution

A

The dissolution of one mineral is accompanied by the precipitation of another

21
Q

Solubility of a mineral

A

The max amount of a compound in a mineral that can be dissolved in solution at a given P-T condition (must be in eq)

22
Q

Mineral solubility constant (Ksp)

A

Chemical reaction constant (K) for the mineral dissolution equation

23
Q

Ion activity product (IAP)

A

The activity of dissolved ions before chemical equilibrium

24
Q

What happens when IAP = Ksp?

A

Saturation

25
Q

What happens when IAP < Ksp?

A

Undersaturation

26
Q

What happens when IAP > Ksp?

A

Oversaturation

27
Q

Geochemical divide

A

When the solution ratio approaches zero. Precipitation stops

28
Q

Solubility diagram

A

A diagram that shows the variation in solubility of a mineral and the change of the dominant dissolved species

29
Q

Mineral stability diagram

A

A diagram that shows the fields in which different minerals are stable

30
Q

How are mineral stability diagrams constructed? (4 steps)

A

1) List all minerals involved
2) Construct the chemical reactions between pairs of minerals
3) Law of mass action to construct activity-activity equations for each pair
4) Plot all activity-activity relations

31
Q

Redox

A

Chemical reaction where electrons are transferred from one species to another

32
Q

Oxidized: _____ electrons

A

Gives away

33
Q

Reduced: _____ electrons

A

Gains

34
Q

Oxidized –> _____ agent

A

Reducing

35
Q

Reduced –> _____ agent

A

Oxidizing

36
Q

True or False: Reduction and oxidation always occur together

A

True

37
Q

Fugacity

A

Effective partial pressure of a gas in a system

38
Q

Oxygen fugacity

A

Effective partial pressure of O2 in a system

39
Q

Eh

A

Redox state of a solution

40
Q

What is the pH equation?

A

pH = -log [H+]

41
Q

What happens when two different geologic fluids encounter each other?

A

They react with one another

42
Q

What happens when a geologic fluid is in contact with a rock?

A

Chemical reaction. Rock will be slightly dissolved

43
Q

How to predict the direction of geochemical reactions?

A

Le Chatelier’s Principle

44
Q

What controls the composition (including Eh and pH) of geologic fluids?

A

Different locations
Different history
Different rocks reacting with one another

Geochemistry (3 decks)

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