ElectrochemistryBy Stephen Rutstein and Danny Verb

Contents1. Oxidation Numbers

2. Balancing Redox Reactions

3. Balancing Half Reactions

4. Electrochemical Cells

5. Cell Potential

6. Nernst Equation and Faraday’s Constant

7. Conversion Factors

8. Corrosion

Oxidation NumbersThe Oxidation number of an element, atom, ion, or

molecule is a representation of its charge.

Elements have an Oxidation Number of 0.

Molecules Oxidation Number sums to 0.

Ions Oxidation Number sums to the ion charge.

The element or ion oxidized is the reducing agent. The element or ion reduced is the oxidizing agent.

Balancing Redox Reactions

Balancing Half Reactions

Balancing Half Reactions

•After splitting the original reaction into two half reactions, you need to balance the molecules by adding water and

hydrogen atoms into the half reactions. •After the molecules are balanced, you must add electrons onto one side of the half reaction to balance the charge.

Balancing Half Reactions

•After balancing the two half reactions, you once again combine them into one half reaction.

Balancing Half Reactions

•Once combined, you can cancel out some of the reactants and products in the reaction if they appear on both

sides of the reaction.

Balancing Half Reactions

•After cancelling out products and reactants, you are left with the final reaction after it has been balanced in an acidic solution.•If needed to be balanced in basic solution, only one additional step is necessary. You must add Hydroxide ions equal to the number of Hydrogen ions. This will cancel out the Hydrogen ions to create another set of water molecules and add Hydroxide ions to the opposite side of the reaction.

Electrochemical Cells

Electrochemical CellsElectron flows goes from the anode to the

cathode through a voltmeter.

The anions within the salt bridge flow from the cathode to the anode to complete the circuit started by the electron flow.

The oxidized ion is the anode and the reduced ion is the cathode in the cell.

Cell PotentialCell Potential is the overall voltage that an

Electrochemical Cell produces.

It is calculated by subtracting the voltage of the anode from the voltage of the cathode.

Nernst Equation and Faraday’s Constant

F = 96,485 Coulombs / mole (of Electrons transferred)

Conversion FactorsQuantity Description Symb

olUnits

Charge Number of Particles

q C = Coulombs

Current “amperage”

Rate of Charge Flow

I 1 Ampere = 1 C / 1 second

Voltage (Potential, emf)

Energy per unit of charge

E 1 Volt = 1 Joule / 1 C

Power Rate of doing work (or of delivering energy)

P 1 Watt = 1 Joule / 1 second

Energy 1 Joule

CorrosionCorrosion is when a metal undergoes a chemical

reaction with its environment. In this reaction, the metal is oxidized to the point that it decays, or breaks down.

A very common form of corrosion is rust. This is the oxidation of iron metal.