alleryStart learning →When one element appears in more than one formula on the same side of an equation, you must:
ASplit the equation in two
BAdd its atoms across the formulas
CBalance that element first
DIgnore the second occurrence
Answer & Solution
Correct answer: B. Add its atoms across the formulas
1. Counting atoms is the whole basis of balancing.
2. If an element appears in more than one formula on a given side of the equation, the number of atoms represented in each must be computed and then added together.
3. Only the total for that side can be compared with the other side.
4. In practice such an element is usually balanced last, not first, for exactly this reason.
5. Ignoring an occurrence would break conservation of atoms.
_Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 4 'Stoichiometry of Chemical Reactions', sections 4.1-4.5_
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