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Electrochemistry Cheat Sheet by

for electrochemistry unit test
cell     electrochemistry     voltaic     oxidization

Oxidation Rules

Neutral Compound = 0 (NO -)
Ion= ion charge (w/ -)
+1 w/ non-metals (Hydrogen)
Oxygen usually -2, -1 in peroxide (H2O2)
-1 w/ metals (H)
Group 1A: always +1
Halogens: usually -1, positive w/ oxygen
Group 2A: always +2
F always -1
Monatomic Ions: made with one atom, same as their charges
EXAMPLE:
 

Redox Equations

Reduction: gain of electrons
Oxidation: loss of electrons
e-: electron
OIL: oxidation is loss (of electrons)
RIG: reduction is gain (of electrons)
OIL as half reaction: Na > Na(+) + e-
RIG as half reaction: Cl + e- > Cl-
for oxidation: e- on right
for reduction: e- is on left
If OX # ^ it is OIL
EXAMPLE:
If OX # goes down it is RIG

Batteries

Defini­tion: a series of voltaic cells that produces a voltage that is the sum of the voltages of the individual cells
Types
Dry Cell Battery: Typical AA, AAA, C, & D
Lead Storage: 12 V (6 cells that each provide 2V)
Anode: Zinc, Cathode: graphite, all immersed in KOH
Anode: Lead, Cathode: PbO2, all immersed in sulfiric acid
Advantage: cheap and small
must be recycled!
Disadv­antage: not rechar­agable
to keep electrodes from touching, wood or glass fiber spacers are used
Rechar­agable Batteris: includes lithium ion, nickel­-ca­dmium, and nickel metal hydride batteries
Voltage may vary as the H2SO4 is used, even after recharging
Built in or separate charger
Advantage: large voltage, can be recharged
Advantage: rechar­gable
Disadv­antage: heavy, expensive, takes up a lot of space
Disadv­antage: cost
Fuel Cells: 2H2(g) + O2 (g) > 2H2O(I)
 
Hydrogen is oxidized, electrons used to create electr­icity
 
Used in spacec­raft, too $$ for general use
 
Adv: no recharge, only emission is water
 
Dis: cost
 

Calcuating Cell Potential

Find correct half reactions on green sheet
Down reduction potential, oxidation more likely (more positive voltage)
Write down half reactions on paper along with voltage
higher voltage is e red, flip other half reaction to make oxidation and change sign given on green sheet (write it backwards)
Add the half reactions and voltages together (e- should cancel)
 

Writing Half Reactions

Assign oxidation numbers
Ex: Zn + Cu2+ > Zn2+ + Cu
Put the atoms with changing oxidation numbers in a separate reaction
Balance all atoms
Balance charge by adding e- to more positive side

Voltaic Cell

Cathode: site of reduction (gaining e-)
Neutral atoms make solid metal
Anode: sire of oxidation (losing e-)
Metal ions can usually dissolve in water
Defini­tion: devices that use a chemical reaction to create electr­icity
Cell Notati­on/­Dia­gram: two half reactions combined
 
Ex: Zn(s)|­Zn2­+(a­q)|­|Cu­2+(­aq)­|Cu(s)

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