zinc carbon cell

i wonder if you're referring to the case that "it is continuously used in short time", or just "used for long time like a week".

in first case, discharge would produce hydrogen gas on the manganese dioxide-coated carbon electrode. manganese is employed to turn the gaseous hydrogen into water, such that bubbles are not formed and block the reaction.

however, rapid discharge of cell produces a lot of hydrogen, which is beyond the capability of manganese dioxide. hydrogen gas forms gas bubbles on graphite electrode, blocking the reaction and thus be not functioning for a short period of time.


in second case, zinc electrode (in form of a metal case) would slowly dissolve and be used up during discharge. after prolonged use, whole zinc case would eventually dissolve and used up. reactant of reaction is used up, so reaction is stopped and the cell becomes unusable.