MCAT General Chemistry Review 7

Oxidation-Reduction Reaction (Redox Reaction)
Electrons are transferred from one atom to another.
Oxidation

An atom that loses an electron

 

Λ H+

Λ O

V Electron

Reduction

Atom gains an electron

 

Λ electrons

V H+

V O

Oxidation State
The possible charge values that an atom may hold within a molecule.
Oxidation States

0 : Atoms in elemental form

-1: Flourine

+1: Hydrogen (except when bonded to a metal when it is -1)

-2: Oxygen (Except when peroxide)

+1: Group 1

+2: Group 2

-3: Group 15

-2: Group 16

-1: Group 17 (Halogens)

 

Reducing Agent
Gives the electron to an atom and is oxidized.
Oxidizing Agent
Atom that is received the electron and be reduced.
Electric Potential, E
Charge transfer resulting from a redox reaction
Half Reaction
One component of a redox reaction
Reduction Potential
Half reaction potential
Galvonic Cell (Voltaic Cell)
Uses the electric potential between phases in a redox reaction to generate a current of electrons from one phase to another in a conversion of chemical energy to electrical energy.
Salt Bridge

Ionic conducting phase of a Galvonic Cell.

Impermeable to electrons.

Terminals
Electron Conductors such as metal wires.
Electrodes

Electronic conductors of a galvonic cell.

Cathode and Anode.

Anode

Marked with a negative sign.

 

Oxidation half reaction occurs here.

Cathode

Marked with a positive sign.

 

Location of the reduction half reaction.

Cell potential, E (Electromotive force)
The potential difference between the terminals when they are not connected.
Free Energy

ΔG=-nFEmax

 

n=moles

F = Faraday’s Constant (96,486 C mol-1)

E = voltage

;

-;G = work done by system, not on the system

+;G = work done on the system

Non standard-state;;G

;G=;GO+RTln(Q)

;

Q=reaction quotient

;GO=Standard State;;G

;

Free Energy at Equilibrium

;GO=-RTln(K)

;

If K=1,;;GO=0

If K ; 1,;;GO;0

If K;1, ;GO;0;

Concentration Cell

A limited form of a galvonic cell with a reduction half reaction taking place in one half cell and the exact reverse of that half reaction taking place in the other half of the cell.

;

Never at standard conditions, so the Nernst equation is needed to solve for the cell potential.

Electrolytic Cell

A galvonic cell with the power hooked up forcing the cell to run backwards.

;

Negative emf.

;

cathode is negative, anode is positive.

reduction still occurs on cathode and oxidation on anode.

;

used for metal plating and purifying.

plating occurs on the cathode.

Current
I = Q/t
Positive reduction potential
Will be reduced
Negative Reduction potential
Will be oxidized.
x

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