I tried to understand how does a battery work. After doing some research, I knew chemical reactions inside are key. But when I came across the reactions inside a zinc carbon battery, almost all websites say "Zinc is oxidized and gives out two electrons".

Why does this reaction happen in the first place? Is it the result of the reaction between the electrolytes and the zinc? And I'm confused what exactly do electrolytes do because I saw they are described as "catalyst". I only understand they allow the flow of ions but prevents the flow of electrons.

Thank you and if what I say above is wrong, please correct me.

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    $\begingroup$ Hi! I'm afraid this would be too broad (i.e. too long) to explain in an answer. You should read up on online tutorials about the basics of electrochemistry. Redox are a series of chemical reactions that just tend to happen. $\endgroup$ – M.A.R. Mar 15 '18 at 6:27

The zinc-carbon cell uses a zinc anode and a manganese dioxide cathode. It is manganese dioxide that takes part in the reaction, not carbon. Carbon is added to the cathode to increase conductivity and retain moisture(catalyst). It also contains a layer of ammonium chloride. Following is the overall reaction. $$ \ce{Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) → Mn2O3(s) + ZnCl2 (aq) + 2NH3(aq)} $$ This is why the half reactions are as follows,

Anode: $\ce{2Zn -> Zn^{2+} + 2e–}$

Cathode: $\ce{2NH4+ + 2MnO2 + 2e– -> Mn2O3 + H2O + 2NH3}$

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. Here, ammonium chloride solution acts as the electrolyte immobilized in the form of a paste. Basically its a chemical medium for flow of charge.

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  • $\begingroup$ I was taught the second reaction instead as $\ce{NH4+ + MnO2 + e- -> NH3 + MnO(OH)}$ Where did you see the one you've written? $\endgroup$ – Gaurang Tandon Mar 15 '18 at 5:57
  • $\begingroup$ Wikepedia says the reaction which you told is when zinc chloride is used . > “If zinc chloride is substituted for ammonium chloride (i.e. replaces ammonium chloride) as the primary electrolyte, the anode reaction remains the same but the cathode reaction is: $$\ce{MnO2(s) + H2O(l) + e− → MnO(OH)(s) + OH−(aq)}$$ $\endgroup$ – MollyCooL Mar 15 '18 at 6:08

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