Electrochemistry Flashcards
Electrochemistry
Chemistry concerned with electron exchange and redox chemistry
Reduction
Gain of electrons
Oxidation
Loss of electrons
How do you get oxidation state/number?
1.) one ion, state = charge
2.) For ions with multiple elements, the states must equal the overall charge
- if it contains these ions, it can affect the
charge
priority increases from bottom to top
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F -1
Group 1/2 metal +1/+2
H +1
O -2
Halogens (Cl, Br, I) -1
Oxidizing agent
Causes something else to oxidize while the agent undergoes reduction
Reducing agent
Causes something else to reduce while the agent undergoes oxidation
Half reaction
Half of a whole reaction showing redox
How to balance a reaction given 2 half reactions?
Multiply so electrons completely cancel out and add rxns together
How to get half reactions?
- Write out net ionic
- Split reactions apart
- Balance moles
How can you balance half reactions and redox reactions?
- Balance half rxns themselves
- Add H2O to balance out O atoms in half reactions
- Add H+ on the other side to balance out the H2O
- Add electrons to either side so the charges can be the same (not 0) on each side
- Add reactions together and multiply so electrons cancel out
How can you balance half reactions and redox reactions in a basic solution?
1) Balance as if in acidic
2.) Add same amount OH as H plus
3.) The OH and H combine to water, and the 14OH adds as normal to the other side
4.) The waters on each side cancel out
How is a current generated?
As a redox reaction happens
Battery
Galvanic/Voltaic cell (spontaneous)
Electrolytic cells
Two half rxns that occur nonspontaneously but are forced to
E oxidation =
-E reduction
How can you decide if something is an oxidation or reduction reaction?
The less positive of the two half rxns will oxidize
How to build a galvanic cell?
- Electrons go from anode to cathode
- Positive ion in the salt bridge go to the cathode and the negative ion goes to anode
- mass anode decreases and conc increases, mass cathode increases and conc decreases; no pH change
Cathode
reduction half cell
Anode
oxidation half cell
Electrode
Conductive surface in the half call, the physical solid in the solution
Cell notation
Abbreviated form of electrochemical cell
electrode(s) - chemical anode(aq) – chemical cathode (aq) - electrode(s)
E cell equation (standard)
(RT/nF)(lnK)
G cell equation (standard)
-RTlnK
Concentration cells
A galvanic cell built on half cells with the same substances
What do amps and F constant equal?
C/s and C/e-
What makes a reaction spontaneous and nonspontaneous?
E cell > 0 (spon)
E cell < 0 (nonspon)
How do reduction potentials affect oxidizing/reducing agents?
The higher the reduction potential, the better the oxidizing agent, and the lower the reduction potential, the better the reducing agent
What makes a cell galvanic or electrolytic?
E cell > 0 (galvanic)
E cell < 0 (electrolytic)
How can you determine if something is oxidizing or reducing?
Identify oxidation states
What are the general rules for a time/amp/mass conversion problem?
1) Change A to C/s
2) Use F constant to convert between C to moles e-
3) To convert to normal moles, balance the half reactions to get moles of e per each element
4) If you are solving for amps be sure to convert back to kj
How can you write out cell notation for an electrolytic cell?
Flip the galvanic cell notation
