The theoretical yield of a component in a chemical reaction is determined by knowing the chemical reaction, balancing it and then using stoichiometry. For example, let us take the case of glucose oxidation:
`C_6H_12O_6 + 6O_2 -> 6 CO_2 + 6H_2O`
here, glucose breaks down to carbon dioxide and water. Since the reaction is well balanced, we can use stoichiometry and see that 1 mole glucose will release 6 moles of carbon dioxide. Assuming that the reaction is 100% complete, we can use the previous statement (from stoichiometry) to determine the theoretical yield of carbon dioxide. By using the molar masses of glucose and carbon dioxide, we can also determine how much carbon dioxide will be generated by a certain quantity of glucose.
We can use the same method for a given reaction involving copper. If we knew the reaction, we can write a well-balanced chemical equation and use stoichiometry to determine the potential yield (by using the molar mass of all the reactants and products).
Hope this helps.