Chapter 17: Electrochemistry Flashcards
what is electrochemistry
branch of chemistry that relates electricity and chemical reactions
what is the easiest method to use when balancing redox rxns
half-reaction method
what is the half-reaction method
- write the oxidation and reduction rxns as separate processes
- balance the 1/2 reactions then combine them
what do you have to do to balance a reaction that occurred in a basic solution?
- add OH- to each side and neutralize the H+ and this will create h2O
what is another name for a voltaic cell and what is it
- separate redox reactions to create a flow of electrons
- galvanic cell and it means spontaneous
what is a half cell
two metals that are not in direct contact with one another
what is an electrode, where does oxidation occur, and where does reduction occur?
- two solid metals that are connected by an external circuit
- oxidation happens at the anode
- reduction happens at the cathode
where do electrons flow in a voltaic cell
- from anode to the cathode
what happens as electrons leave the anode
- cations dissolve into the solution of the anode compartment
- anode loses mass, the solution becomes more concentrated
what happens the cathode as electrons enter it
- cations in the solution are attracted to the negative cathode
- electrons transfer the cations forming neutral metals
- cathode gains mass and the solution becomes less concentrated
what is a salt bridge and what would happen if we didn’t have one
- u shaped tube that contains salt solution to keep the charges balanced
if we didn’t have a salt bridge the charges would not be balanced and the flow of electrons would stop
what ions are a salt bridge composed of
ions that will not react with the other ions in the cell or with the elctrode
where do anions move towards
where do cations move towards
- move toward the anodes (-)
- move toward the cathode (+)
what is cell notation
- shorthand description of a voltaic cell
electrode| electrolyte || electroltye|| electrode
what does | mean in a voltaic cell
what does || mean
what does , mean
- phase barrier
- || = salt bridge
- = ,= used if multiple electrolytes are in the same phase
what direction do electrons flow spontaneously
in one way bc of the difference in potential energy
flow from the anode to the cathode bc the PE of electrons is higher in the anode than the cathode
what is potential difference
the difference in PE per electrical charge
what is the electromotive force (emf)
units = Volts or V
the potential difference in a cell between the anode and cathode
- it is also called the Ecell
what is a voltmeter and how does it work
what will the cell potential be for a spontaneous reaction
cell potential will be positive because Ecell is measured in volts
what does emf of a voltaic cell depend on
the cathode and anode half cells involved
emf is also called cell voltage
what is the oxidzing agent
what is the reducing agent
what does Ered refer to
the standard conditions for the electrode for reduction reactions
what is the standard hydrogen electrode (SHE)
- the reduction of H+ to H2 under standard conditions
H2 (g) at 1 atm and and an acidic solution with [H+] = 1M
how many volts does SHE equal
0 V
what does SHE consist of
an electrode with a finely divided Pt(platinum) in contact with H2
what happens when SHE is the cathode
what happens when SHE is the anode
- cathode of a cell then the two H+ ions each accept an electron from the Pt electrode and are reduced to H atoms
- anode H2 molecules lose two electrons and are oxidized to H+
why is standard potential an extensive property
it is based the amount of energy per unit of charge
increase the substances then we would increase the energy
what is the standard cell potential equation
Ecell = Ered(cathode / reduction)+ -(red(anode/ oxidation))
what is the Ered for strong oxidizers
- the strongest oxidizers have the most positive Ered
- have a greater tendency for the reactant of the 1/2 rxn to be reduced and oxidize another species
what is the E red for strong reducers
- they have the most negative E red
- half rxn w/ the smallest Ered is the most easily reversed as an oxidation
Ered =
red(red)-red(ox)
what is the equation for cell potential and electric work
E = -w/q and q = nF
q = quantity of charge in C transferred
n = moles of electrons
F = faraday = 96485 C/mol e^-
how is work related to free energy
G = wmax = -qEmax = -nFE
what happens as a voltaic cell is discharged
the reactants are consumed and the products are produced
* the concentrations of the reactants and products are not constant*
emf = 0 meaning it is considered dead and it is at equilibrium
what is the nernst equation
emf generated under nonstandard conditions can be calculated using the nernst equation
what is the nernst equation
E = 0.0592V/ n logk
what are the conditions for a spontaneous rxn
G = negative
K = positive
E = positive
