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Is the number of moles of an element reacted equal to the number of moles of an element produced?

-Let's say for example, 5g of copper. So the molar mass of copper (according to my textbook in which I need to use those numbers) is 63.55g/mol

So 5g / 63.55g/mol = 0.08mol

So that means that 0.08 mol of copper reacted, as well as 0.08 mol of copper was produced. Am I correct?

As long as you're careful what you are equating I would say yes.

4Cu + O2 ==> 2Cu2O
So you have 4 mols Cu atoms on the left and 4 mols Cu atoms on the right. BUT you have 4 mols Cu atoms on the left and only 2 mols Cu2O on the right. Also note that you mols are not conserved. You hae 5 total mols on the left and 2 total mols on the right.

So the number of moles on the left side would have to equal the number of moles on the right side of the equation? And does this apply for the total number of moles on one side, or just the number of moles of one element on one side?

So the number of moles on the left side would have to equal the number of moles on the right side of the equation?For the same element yes And does this apply for the total number of moles on one side, or just the number of moles of one element on one side? I don't know what you mean by total number of moles on one side or just the number of moles of one element on one side?.

The total number of moles ON ONE SIDE, it appears to me, can be any number we choose and the total number of moles of one element on one side can be anything. As I wrote above, however, total mols on one side need not equal total mols on the other side.

Yes, you are correct. The number of moles of an element reacted is equal to the number of moles of an element produced, according to the law of conservation of mass. In this example, you have correctly calculated that 5 grams of copper is equal to 0.08 moles, using the molar mass of copper. Therefore, 0.08 moles of copper have reacted, and as a result, 0.08 moles of copper have been produced. The reaction does not create or destroy any copper atoms, only rearranges them, so the number of moles remains the same.