Batteries Use Electrochemical Reactions to Produce a Ready Supply of Electric Current

6 Batteries Use Electrochemical Reactions to Produce a Ready Supply of Electric Current 

Layer of Mn02 Graphite cathode Zinc anode 

A carbon rod serves as the cathode, which is immersed in the electrolyte in the center of the cell. The cell reactions are 

Because the ions Ag and Cl cannot exist separately in solution, the individual activity coefficients of these ions are not separately defined. Instead we define a mean activity y , which in this case is the geometric mean of the individual activity coefficients y = VyAg+ ycr For rn n electrolyte (a compound composed of cations of charge m+ and anions of charge rf, for example, MgCl2 is a 2 1 electrolyte), the mean activity coefficient is y = The mean activities for ionic compounds can be estimated 

Actually, this equation is an oversimplification of a complex process. The voltage produced by this dry cell is about 1.5 V, but this voltage will decrease somewhat over time because, as the reaction proceeds, the concentration NHj (aq) will decrease and NHsCfl ) will decrease, leading to an increase in the value of 2 the Nerst equation and a decrease in the emf of the cell. The other species in the overall reaction are present in pure liquid or solid form and do not affect Q. 

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