Chemistry Essay: Electrochemical Cells
By John Williams
An electrochemical cell is s cell in which chemical energy in a redox reaction is converted to electrical energy. It consists of two half cells connected internally by a salt bridge and externally by wires. A hydrogen half cell is the standard electrode and all comparisons of the other half cells are made against this half cell which has an E( value of zero volts. The E( values of other half cells are obtained by measuring the total emf (electromotive force/Eocell) when attached to a standard hydrogen electrode. All standard reduction potentials are measured with a solution concentration of 1 mol L-1, gas pressures of 101.3 kPa and at a temperature of 25(C (except for #). A table of standard reduction potentials has been recorded so the E( values of half reactions can be accurately known and referred to.
– Anode: The electrode where oxidation occurs. Electrons move away from the anode. – Cathode: The electrode where reduction occurs. Electrons are “pulled” towards the cathode. – These electrodes (anode and cathode) are linked by an external wire which enables electron flow between the two solutions. – Salt bridge: A salt bridge contains non reactive electrolyte which prevents direct contact of the oxidising and reducing agents as well as stopping the cell from polarising.
A primary cell is an electrochemical cell or battery that cannot be recharged and has a reaction that can’t be reversed for any number of reasons and consequently renders the cell unrechargable. It is designed to be used once and then discarded. As a primary cell is used, chemical reactions in the battery use up the chemicals that generate the power; when they are gone, the battery stops producing electricity and is useless. A major factor reducing the lifetime of primary cells is that they become polarized during use.
The Leclanche or Dry cell is a primary cell. It consists of a zinc can which is...