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Amount of energy required to purify copper using electrolysis?

The purification of copper by electrolysis involves an anode of impure copper and a cathode of pure copper. During the electrolysis, copper (II) ions leave the anode slab and plate onto the cathode slab.

The reaction at the anode is Cu(s) = Cu2+(aq) +2e-
The reaction at the cathode is Cu2+(aq) + 2e- = Cu(s)

Therefore, it would appear that these two reactions cancel out leaving an emf of zero.

I don't understand how you can calculate the amount of energy required to purify copper being that the emf is zero.

How much energy (in joules) is required to purify a given amount (i.e. 100g) of copper?

Is heat produced? Why or why not? If so, how much (heat)?