Topic 6- Electrochemistry Flashcards
Electrochemistry
interchange of chemical and
electrical energy
Redox reaction
Chemical reaction involving the transfer of electrons
from one species to another
OIL RIG
Oxidation Involves Loss- e on prod
Reduction Involves Gain - e on reac
-must match
During redox reactions, the oxidation numbers of the atoms change
Oxidation is an increase in oxidation state
* Reduction is a decrease in oxidation state
numbers/ charges for: elements alone, monatomic, group 1, group 2, hydrogen, oxygen, group 17
-alone= 0
-montomic= same as its charge
-G1=+1
-G2= +2
-H= usually +1, but -1 with metals
-O= usually -2 but -1 with peroxides element + O-O
-group 17= -1
Redox reaction occur between
oxidizing and reducing agent
-reduction agent= the giver (oxidized)
-oxi agent= taker (reduction)
Balancing Half reactions
- Separate into half reactions and balance individually
- Equalize electrons in the half-reactions
- Add the half-reactions back together (electrons should cancel)
Balancing under acidic conditions
- Assign oxidation numbers/state
2.Write oxidation and reduction half-reactions - Balance elements for each half-reaction:
-All elements EXCEPT H and O
b. Balance O using H2O
c. Balance H using H+
d. Balance charge using electrons
4.Balance number of electrons gained and lost in the half-reactions
by multiplying the reactions by coefficients
- Add half-reactions together and cancel identical species
- Check that elements and overall charges balance
one thing to check when doing reaction to see if right
the charges at the end add up
Balancing under basic conditions
Do all steps for balancing in acidic solution, then
7.Add OH- to both side of equation to use up H+
8. Form H2O if H+ and OH- are on same side of equation
9. Cancel H2Oβs which are on both sides
10. Check element and charge balance
Voltaic/Galvanic cells
-Electric cells used for scientific study
-Energy released in a spontaneous redox
reaction can be used to perform
electrical work
-eg battery
Galvanic cells are composed of two
half reactions
-need a salt bridge for current to take place
-electrodes: anode and cathode (anox and redcat)
-anode goes to the cathode
Galvanic cell shorthand notation
anode I electrolyte A II electrolyte C I cathode
-charges in middle
-dont need to worry about charges
Standard electrode potentials
The anode must
have a higher
potential energy
than the cathode!
Cell potential
-Cell Potential (πΈππππ ): The potential difference between electrodes in a
galvanic cell
-driving force that pushes electrons through the
external circuit.
-positive (spon)
-intensive party
-Measured in Volts
intensive party for volts
does NOT depend on the amount of substance
-IGNORE COEFFICIENTS
cell potential at standard conditions πΈππππ formula
πΈππππ= πΈπππ‘βπππβ πΈπππππ
can only measure the difference between two half-cells
Highest EΒ° β Cathode (gets reduced)
Lowest EΒ° β Anode (gets oxidized)
relate πΈππππ π to βπΊ
βπΊπ β ππΉπΈππππ
Nernst equation
πΈππππ = πΈπππππ β π π/ππΉ x ln π
NON standard- temp over 25, 1.0 M
n=number of electrons
if Q=1 then
e cell= e cell β
at equilibrium Ecell =
0, Q=K
0= Ecell -RT/nF Ln K
Consider an electrochemical cell that has a redox reaction with πΎ = 0.10.
This cell is under nonstandard conditions such that π = 0.0010. What does this mean
K= will always be neg
if Q<K, goes to products therfore postive
E cell pos, E cell β is neg
concentration cell questions
where both sides have the
same half reaction but different concentrations
concentration= 0 volts
go over last slide for integrated question
slide 60
