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Redox + Cells

Oxidation and Reduction involves electron transfer.

Oxidation is Loss of Electrons.

Reduction is Gain of Electrons.

For the electron transfer during a redox reaction we can construct a overall equation for the redox reaction once if we know the oxidation and reduction half equation.

Cells + Half Cells

An electrochemical cells creates energy from redox reactions. It controls the electron transfer to make electrical energy. This is the basis of most cells (a.k.a batteries)

Half Cells consist of an element in two oxidation states, the simplest half cells are made from metal placed in a solution of its aqueous ions.

Types of Half Cells

Metal/Metal Ion Half Cells

A simple electrochemical cell can be made by connecting two of these type of half cells but they must have different electrode potentials.

One half cell will then release the electrons and one will gain, the difference in electrode potential is measured with a voltmeter

Non-Metal/Non-Metal Ion Half Cells

An example of one of these half cells is the hydrogen half cell where hydrogen gas, the non-metal, is bubbled through concentrated acid, which contains the metal ion H+. One problem with this type of half cell is there is no solid electrode to connect a wire too so to overcome this a platinum electrode is place in the aqueous solution at the interface where the gas and acid meet.

Metal Ion/Metal Ion Half cells

This type of half cell consist of the same element in different oxidation states and are in aqueous form so again a platinum electrode has to be used.

Cell Potentials

Standard electrode potentials are the potential voltage of a half cell relative to the standard hydrogen electrode under standard conditions.

Chemist can calculate cell potentials under standard conditions, they measure the cell against the know standard hydrogen half cell which is used as a reference to measure against with all other half cells. The hydrogen cell has a standard electrode potential of 0.00V.

The standard electrode potential can be used to calculate the full cell potential and the feasibility.

For example, A Cu cell has a standard electrode potential of +0.34V. A Zn half cell has a standard electrode potential of -0.76 but this is reversed as…

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