Aqueous Geochemistry

Question 1

Physical geologic processes

Answer 1

With or without participation of geofluids

Question 2

Chemical geologic processes

Answer 2

Participated by geofluids

Question 3

Composition of geofluids

Answer 3

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

Question 4

Dissolved species

Answer 4

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

Question 5

What reaction is always in the background?

Answer 5

H2O = H+ + OH-

Question 6

Dissolved components

Answer 6

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

Question 7

Avogadro’s number

Answer 7

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

Question 8

Molality (m) is = to what?

Answer 8

moles / kg water

Question 9

Molarity (M) is = to what?

Answer 9

moles / liter solution

Question 10

What are the two types of geochemical reactions?

Answer 10

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

Question 11

Open system

Answer 11

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

Question 12

Closed system

Answer 12

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

Question 13

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

Answer 13

True

Question 14

Chemical reaction equilibrium

Answer 14

Forward reaction rate = Reverse reaction rate

Question 15

Le Chatelier’s Principle

Answer 15

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

Question 16

Difference between concentration and activity

Answer 16

Concentration: (A)
Activity: [A]

Question 17

Law of mass action equation

Answer 17

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

Question 18

How is equilibrium constant K determined?

Answer 18

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

Question 19

Congruent dissolution

Answer 19

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

Question 20

Incongruent dissolution

Answer 20

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

Question 21

Solubility of a mineral

Answer 21

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)

Question 22

Mineral solubility constant (Ksp)

Answer 22

Chemical reaction constant (K) for the mineral dissolution equation

Question 23

Ion activity product (IAP)

Answer 23

The activity of dissolved ions before chemical equilibrium

Question 24

What happens when IAP = Ksp?

Answer 24

Saturation

Question 25

What happens when IAP < Ksp?

Answer 25

Undersaturation

Question 26

What happens when IAP > Ksp?

Answer 26

Oversaturation

Question 27

Geochemical divide

Answer 27

When the solution ratio approaches zero. Precipitation stops

Question 28

Solubility diagram

Answer 28

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

Question 29

Mineral stability diagram

Answer 29

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

Question 30

How are mineral stability diagrams constructed? (4 steps)

Answer 30

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

Question 31

Redox

Answer 31

Chemical reaction where electrons are transferred from one species to another

Question 32

Oxidized: _____ electrons

Answer 32

Gives away

Question 33

Reduced: _____ electrons

Answer 33

Gains

Question 34

Oxidized --> _____ agent

Answer 34

Reducing

Question 35

Reduced --> _____ agent

Answer 35

Oxidizing

Question 36

True or False: Reduction and oxidation always occur together

Answer 36

True

Question 37

Fugacity

Answer 37

Effective partial pressure of a gas in a system

Question 38

Oxygen fugacity

Answer 38

Effective partial pressure of O2 in a system

Question 39

Eh

Answer 39

Redox state of a solution

Question 40

What is the pH equation?

Answer 40

pH = -log [H+]

Question 41

What happens when two different geologic fluids encounter each other?

Answer 41

They react with one another

Question 42

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

Answer 42

Chemical reaction. Rock will be slightly dissolved

Question 43

How to predict the direction of geochemical reactions?

Answer 43

Le Chatelier's Principle

Question 44

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

Answer 44

Different locations Different history Different rocks reacting with one another