CHE 2C Midterm 1

1st OS rule

groups 1 and 2 have charge of group number. No exceptions.

2nd OS rule

H is +1 except H2= 0 and metal hydrides (NaH/CaH, os H = -1)

3rd OS rule

O is -2 except O2, O3 = 0 and peroxides (H2O2, O os = -1 and OF2, os = +2)

4th OS rule

F is -1 except F2 = 0

5th OS rule

Halides (Cl, Br, I) = -1 except when bonded to O or F (HClO4, Cl os = +7)

Good salt bridge ions

Na+, K+, Cl-, NO2-

what makes a good salt bridge ion

Soluble, not reactive with the electrodes or species in solution

good inert electrodes

P+, C (graphite)

Cell diagram notation

anode 1st then cathode, || = salt bridge, | = phase change, comma would separate different species in same phase, use electrode if no solids (must start and end with a solid), read left to right reactant to product, no spectator ions.

standard reduction potentials table

higher = more “positive”, strong oxidants (oxidizing agent) (take e-), is reduced
lower = more “negative”, strong reductants (reducing agent) (donate e-), is oxidized

E°cell > 0

spontaneous

E°cell < 0

not spontaneous

E°cell = 0

at equilibrium

E° indicates?

standard state (1M), P = 1 atm, at 25° C

-ΔG

spontaneous

+ΔG

not spontaneous

ΔG = 0

at equilibrium

primary batteries

Not rechargeable, high power, longer lasting, inexpensive

primary battery example

Dry cell, named Leclanche for its inventor

secondary batteries

rechargeable for many cycles (run cell in reverse by electrolysis to recharge)

secondary battery example

Lead-acid battery, lithium ion battery

fuel cells

must provide fuel in continuous supply (can use different fuels: H₂ is the lightest)

corrosion process

spontaneous (fast or slow), undesirable redox chemistry

corrosion example

(anode) Fe_(s) → Fe²⁺_(aq) + 2e^- (cathode) O_2(s) + 4H⁺_(aq) + 4e^- → 2H₂O_(l)

1st corrosion prevention

create protective layer (paint or already oxidized material; statue of liberty)

2nd corrosion prevention

mix in some corrosion resistant metals

3rd corrosion prevention

physically connect a sacrificial anode to the system (sacrificial = will donate its own e- first, protecting another metal)

pH = ?

-log[H⁺]

[H⁺] =

10^-pH

n_e = ?

total moles of e^- used

I = ?

current, usually amps (c/s)

F (in faraday’s law)

96485 c/mol

galvanic cell

spontaneous, chemical energy turns into electrical energy, wide range of anode/cathode combos possible, cell potential determined from E_red of half cells, often 2 different half rxns. Flows: anode e^-→e^- cathode. anode: [M⁺] increases (solid decreases). cathode: [M⁺] decreases (solid increases).

Concentration cell

type of galvanic cell, same half rxns in cathode and anode, different concentrations drive the cell toward equilibrium (equal concentrations). (anode) xM[M⁺] <<yM[M⁺] (cathode)

Electrolytic cell

non spontaneous, electrical energy turns into chemical energy, powered with current, metal ions from solution (or other products) form at the electrode, some similarities to the cathode of a galvanic cell, E_red determines which product forms if multiple possible. Flows: cathode e^- ← e^- anode

anions(-) go to the

anode

cations(+) go to the

cathode

in the external circuit e- migrate

from the anode to the cathode

oxidized is

anode

reduced

cathode