13 Oxidation-Reduction and Electrochemistry Flashcards
The oxidation state of an atom that is not bonded to an atom of another element is
zero. That means either an atom that is not bonded to any other atom or an atom that is bonded to another atom of the same element.
the oxidation numbers for all the atoms in a molecule must
add up to zero.
The oxidation numbers for allt he atoms in a polyatomic ion must add up to
the charge of the ion.
Oxidation Numbers:
Alkali Metals (Li, Na, . . .)
+1
Oxidation Numbers
Alkaline Earths( Be, Mg, . . .)
+2
Oxidation Numbers
Group 3A (B, Al, . . .)
+3
Oxidation Numbers
Oxygen
-2
Oxidation Numbers
Halogens (F, Cl, . . .)
-1
Hydroxide
OH-
Nitrate
NO3-
Perchlorate
ClO4-
Acetate
C2H3O2-
Carbonate
CO32-
Sulfate
SO42-
Phosphate
PO43-
When an atom gains electrons, its oxidation number
decreases, and it is said too have been reduced.
Reduction is Gain
When an atom loses electrons, its oxidation number
increases, and it is said to have been oxidized.
Oxidation is Loss
If an atom is losing electrons and being oxidized, it must be giving the electrons to another atom, which is being reduced. So if a reactant contains an atom that is being oxidized,
it is a reducing agent or a deductant
If an atom is taking electrons and being reduced, it must be taking electrons away from another atom, which is being oxidized. So if a reactant contains an atom that is being reduced, it is an
oxidizing agent or oxidant.
{Delta}Gº =
-nFEº
{Delta}Gº = Standard Gibbs Free energy change (kJ/mol)
n = the number of moles of electrons exchanged in the reaction (mol)
F = Faraday’s constant, 96,500 coulombs (that is 1 mole of electrons has a charge of 96,500 coulombs)
E = Standard reaction potential (V)
If Eº is positive, {Delta}Gº is
negative and the reaction is spontaneous, and if Eº is negative, {Delta}Gº is positive and the reaction is nonspontaneous.
E =
(RT/nF)lnk
E = standard reduction potential
R = the gas constant, 8.31 (volt-coulomb)/ (mol-K)
T= absolute temperatuer (K)
n = the number of moles of electrons exchanged in the reaction (mol)
F = Faradyay’s constant, 96,500 coulombs/mole
K= equilibrium constant
Oxidation takes place at the electrode called the
anode. Reduction takes place at the electrode called the cathode.
AN OX
RED CAT
As the concentration of the products of a redox reaction increases, the voltage
decreases; and as the concentration of the reactants in a redox reaction increases, the voltage increases.
In an Electrolytic cell, an outside source is used to force
a nonspontaneous reaction to take place.
In a galvanic Cell a spontaneous
redox reaction is used to generate a flow of current
I =
q / t
I = current (amperes)
q = charge (coulombs, C)
t = time (sec)
Current is defined as the flow of
positive charge, so current is always in the opposite direction from the flow of electrons.
In a galvanic cell,
a spontaneous redox reaction is used to generate current.
At 25º C(298K), the Voltage Equilibrium equation simplifies too
log K =
nEº / 0.0592
To calculate the potential of a redox reaction;
Add the potential for the oxidation half-reaction to
the potential for the reduction half reaction
Never multiply the potentiial for a half-reaction by a coefficient
1 mole of e- =
1 Faraday
