Week 3

Question 1

What is an example of a weathering reaction? how does it work?

Answer 1

albite to kaolinite
a cation-rich primary mineral (e.g. albite) reacts with a weak acid (CO2 in rain) to give a CATION-POOR CLAY MINERAL (e.g. kaolinite) and various ions dissolved in rain water

Question 2

Where do Mn nodules form?

Answer 2

abyssal plains
low productivity areas

Question 3

what does pyrite reduce to?

Answer 3

galena PbS

Question 4

Major anions?

Answer 4

Cl-, SO4 2-, HCO3 -

Question 5

Major cations?

Answer 5

Na+, Mg 2+, Ca 2+, K+

Question 6

No significant change in the order of ________ over past 900 Myrs

Answer 6

salt precipitation

Question 7

Ions in seawater have been about the same composition for the past _____ years

Answer 7

1 billion

Question 8

North Atlantic has low or high pH?
Youngest or oldest deep water?
Low or high CO3?

Answer 8

high
youngest
high

Question 9

North Pacific has low or high pH?
Youngest or oldest deep water?
Low or high CO3?

Answer 9

low
oldest
low

Question 10

mineral formed in anoxic conditions?

Answer 10

pyrite

Question 11

most abundant ion in seawater

Answer 11

chloride

Question 12

most abundant sulfate salt in evaporites

Answer 12

gypsum

Question 13

originally released as mantle volatiles

Answer 13

anions

Question 14

total amount divided by input or output

Answer 14

residence time

Question 15

most abundant mineral in evaporites

Answer 15

halite

Question 16

mineral formed in high productivity areas

Answer 16

phosphorite

Question 17

exchanges with sodium in estuaries

Answer 17

calcium

Question 18

correlates with phosphate

Answer 18

cadmium

Question 19

Why do we use “Marine chemistry units”: moles solute / kg seawater

Answer 19

seawater is compressible at depth and the volume varies slightly with depth, so we use mass (not volume) in the denominator

Question 20

Thermodynamics is

Answer 20

the energetics of reactions
most species are at equilibrium in seawater

Question 21

kinetics is

Answer 21

how fast reactions proceed. activation energy is a factor
most species are kinetically controlled in the atmosphere

Question 22

equation for the reaction coefficient

Answer 22

for reaction A+B -> AB
K = [AB] / [A]*[B]

Question 23

If delta H is negative the reaction ____ heat

Answer 23

releases

Question 24

if delta s is negative the reaction randomness _____

Answer 24

decreases

Question 25

if delta g is negative, the reaction is _____

Answer 25

spontaneous

Question 26

Usually, the solubility of solid salts in water _____ with temperature while the solubility of gases _____

Answer 26

increases
decreases

Question 27

A reaction whose delta G = -100 kJ/mol is

Answer 27

spontaneous

Question 28

You are asked to predict if the following reaction is spontaneous at 100°C:
N2(g) + 3 H2(g)  2 NH3(g) How would you go about answering this?
a) Look up ∆G° for each compound, and use ∆G°=∆G°prod - ∆G°react
b) Use the equation ∆G = -RT lnKeq

Answer 28

b) Use the equation ∆G = -RT lnKeq

Question 29

as you heat up a liquid, what happens to the solubility of a gas in the liquid?

Answer 29

it goes down

Question 30

Why are Cd/Ca ratios in benthic forams of interest for knowing past ocean chemistry?

Answer 30

Cd/Ca correlates with nutrient concentrations in seawater, and can help determine past ocean circulation changes

Question 31

What is the process that causes nutrient concentrations in deep sea water to increase from the North Atlantic to the North Pacific?

Answer 31

respiration or decomposition