necessity to memorise half equations

[hippo326]

anyone got an idea if that would be a waste of time memorizing all those half equations for primary cells and secondary cells ?

[roly182]

waste of time.. its not exprected knowledge. Know how to derive half equations from the whole equation though and vice versa

[hippo326]

thanks..but not even the important ones say like car batteries and hall cells?

[roly182]

Oh sorry, yeah it might be a good idea to be familiar with the half equations for the lead acid accumulator, hydrogen-oxygen fuel cell, hall-heroult and downs cell. I doubt if they would ask you to write the equations from scratch.. more likely to give you it and ask you to interpret it.. example.. write oxidation reaction, which species is acting as the reductant and so on. I would rather concentrate on learning about the cells.. such as why is a high current used in the hall cell or why is the electrolyte in the down cell impure and so on..

[lanvins]

Know how to derive half equations from the whole equation though and vice versa

Could you give an example of this?

[roly182]

Sorry i havn't learnt how to use syntax....

Consider the reaction:
2H₂ + O₂ --> 2H₂O

write the equations for oxidation and reduction

Or it could give you both equations for oxidation and reduction and ask you to write the above equation. Similiar to the first question on the sample exam.

Its more likely this sort of question will be for reactions you are not familiar...

Li + CoO₂ --> LiCoO2

Oxidation : Li --> Li⁺ + e^-

Now write the reduction reaction... stuff like that!

[shinny]

Grab your textbook and find the one for the lead acid accumulator, and work backwards purely from that reaction to find the two half equations. If you can do that one, you'll be set for anything =T