H.1 Chemical Principle 7th edition

[Ziyan Wang 3J]

H.1 It appears that balancing the chemical equation Cu + SO2-> CuO + S would be simple if we could just add another O atom to the product side: Cu + SO2 -> CuO + S +O. (a) Why is that balancing procedure not allowed? (b) Balance the equation correctly.

[Maya Gollamudi 1G]

We can't add O to the equation because oxygen is not one of the products produced in this chemical reaction.

The correctly balanced equation would be 2Cu + SO2 --> 2CuO + S.

[Vanessa Chuang 4F]

a) You can't just add elements to the product side if the reaction doesn't actually produce it (as stated in law of conservation of mass). In this case, O isn't actually produced from this equation so you wouldn't be allowed to just create it out of nowhere.
b) 2Cu +SO2-> 2CuO +S

[KarineKim2L]

As the person above said, O is not a product of the reaction. Having 2 moles of CuO is very different from having an extra O atom. Also, typically in reactions, single O atoms are not produced.

[Nyari Muchaka_Discussion 4A]

Matter cannot be created or destroyed so if oxygen isn't present(on its own) in the reactant side if cannot just show up on the product side. Hence why we balance equations, to ensure the same number of reactants is present in the products.
2Cu +SO2-> 2CuO +S