Electrochemical Cells - oxidants and reductants

[Da Apprentice]

In an electrochemical cell involving copper and magnesium copper gains electrons (is the oxidant) and Magnesium the opposite. I understand that Cu is the least reactive of the two electodes and therefore the Mg gives up electrons to stop the Cu from oxidising, but why does this difference in reactivity encourage the Mg to lose electrons? and also why is cu considered the least reastive of the two electrodes? Cu has only one valency electrode where as Mg has two so therefore shouldn't it require less energy to exchange Coppers one electron than magnesiums two?

Thanks,

 

[Nemus]

You haven't quite got it right in a few places.
First:
Cu2+ is normally what you get not Cu+.
Second:
First look at the two processes independently:
Mg <-> Mg2+ + 2 e-
Cu <-> Cu 2+ + 2 e-
For detailed reasons about energy levels and solvation Mg is more prone to give off its electrons. This can be looked up in standard electrode potential tables. If you then connect the two systems with a wire the extra electrons from the Mg electrode will flow towards the copper electrode.Did that help?