The half-reactions areĢMnO 2(s) + H 2O(l) + 2e -> Mn 2O 3(s) + 2OH -(aq) Potassium hydroxide is a base or alkaline material, hence "alkaline" batteries. BatteriesĪlkaline cells overcome some of the problems with carbon-zinc batteries by using potassium hydroxide in place of ammonium chloride in the electrolyte. While these batteries have a long history of usefulness, they are declining in application since some of their problems are overcome in alkaline batteries. Oxidation of the zinc wall eventually causes the contents to leak out, so such batteries should not be left in electric equipment for long periods. It also has a short shelf life and deteriorates rapidly in cold weather. The voltage of this cell is initially about 1.5 volts, but decreases as energy is taken from the cell. Zinc chloride reacts with ammonia to form solid zinc ammonium chloride and manganese dioxide reacts with hydrogen to form solid dimanganese trioxide plus water (Hewitt). That is accomplished with two further reactions in the paste electrolyte. Which must be absorbed to prevent the buildup of gas pressure. Some of the complexity of this reaction comes from the fact that the reduction of the ammonium ion produces two gaseous products The chemical reactions in this cell may be approximated byĢNH 4 +(aq) + 2MnO 2(s) + 2e -> Mn 2O 3(s) + H 2O(l) + 2NH 3(aq) The other reactions involve the MnO 2 which is contained near the carbon center rod and the NH 4Cl and ZnCl 2 which make up the bulk of the paste between the cathode and anode. The oxidation at the zinc electrode (the anode) is straightforward and similar to that in other cells like the Daniell cell. The venerable carbon-zinc cell or Lechlanche' cell was invented in 1866 and was the most common small battery throughout most of the 20th century until largely supplanted by alkaline cells. HyperPhysics***** Electricity and Magnetism Voltages generated by such cells have historically been referred to as emf (electromotive force). An electrochemical cell which produces an external current is called a voltaic cell. The basic element is called an electrochemical cell and makes use of an oxidation/reduction reaction. Batteries use a chemical reaction to do work on charge and produce a voltage between their output terminals.
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