chapter 8 part 2 Flashcards
standard reduction potentials
standard state: 1.0 M, 1.0 atm, 25 degrees Celsius
standard reduction potential
the driving force of the reduction half-reaction
reduction potential is a positive value
standard oxidation potential
the driving force of the oxidation half-reaction
oxidation is the reverse of reduction, therefore, oxidation potential is a negative value
increased potential as oxidizing agent
increased potential as reducing agent
increased positive value
increased negative value
if cell potential is positive, the reaction is
if cell potential is negative, the reaction is
if cell potential is 0, the reaction is
spontaneous
nonspontaneous
equuilibrium
as a spontaneous reaction occurs, it will leave standard state and e cell potential will
decrease until it reaches equilibrium
e cell potential equation
e cell 0 = -e cell reduction (oxidation) + e cell reduction 0
would it be wise to store 1.0 M KMnO4 in an iron storage tank at 25 degrees storage?
No, a spontaneous REDOX reaction occurs between the permanganate and the solid iron container. the storage tank would corrode
what metals can be oxidized by Al3+ cations under standard conditions?
reduction e cell = -1.66 V
any metals with an oxidation potential > +1.66 V will form a (+) e cell potential
Na or Li. the aluminum will reduce to Al0 and the metals will oxidize to +1
what will happen when you put Cu metals in AgNO3 solution?
a strip of Cu metal placed in AgNO3 solution will result in silver metal and copper nitrate solution
rusting of iron in aqueous solution,
the iron (II) hydroxide is reasonably
Fe(OH)2 is rapidly oxidized by
Fe0 is readily oxidized to Fe2+
soluble in water
oxygen to Fe2O3
disproportion
thermodynamically spontaneous but kinetically slow
can electrochemically react with itself
kinetics can be influenced by
your body uses the enzyme ? to remove dangerous peroxides
catalysts
catalase
Latimer diagrams
a diagram that allows for a comparative investigation of REDOX potential
electrochemical products of rusting are
why does rusting occur faster near oceans or where roads are salted?
Fe(OH)2 and Fe(OH)3
the ionic conductivity of the water promotes flow of electrons
in well oxygenated water, the ultimate product is
in poorly oxygenated water, the ultimate product is
Fe2O3 and FeO(OH) (can form rusticles)
Fe3O4
Pourbaix (Eh-pH) diagrams are used to
study thermodynamically stable species relative to cell potential and pH
Vertical Lines
Horizontal Lines
High Eh
Low Eh
equilibrium independent of potential
equilibrium solely dependent on potential. independent of pH
oxidized species
reduced species
towards top
towards bottom
ph 0-7
pH 7-14
oxidizing conditions
reducing conditions
acidic conditions
basic conditions
why is zinc metal attached to underground iron pipes?
the O2 will oxidize the zinc metal over iron metal. once all zinc is oxidized, the O2 will begin to oxidize the iron
iron is dipped into molten zinc. the zinc diffuses into the outer Fe-layers forming a
a dense non-conducting surface of ? forms. preventing ?
Zn-Fe alloy
ZnO forms; oxidation in air
if ZnO layer is penetrated, the zinc
galvanization of iron makes the object
corrodes preferentially to the iron
more resistant to corrosion
an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte
galvanic corrosion
faraday’s constant
9.65*10^4 C/mole of electrons
nernst equation
corrects for temperature and concentration
R ideal gas constant
8.314 VC/Kmol
electrochemistry
study of chemical changes provided by electrical current and the production of electricity by chemical means
galvanic (voltanic) cell
examples
spontaneous chemical reactions create electricity
batteries and fuel cells
electrolytic cell
examples
input electrical energy causes a nonspontaneous reaction to occur
refining, battery charging, electroplating
electrode
the electrode must be a
a conducting surface where the oxidation/reduction occurs
conductive material. usually metallic or graphite
the chemical species in the half reaction are present
in each half cell
