A chemical equation can be used to solve stoichiometry problems provided that it

Stoichiometry uses the mole ratios between substances, and those ratios come from the coefficients in a balanced chemical equation. For example, in 2H₂ + O₂ → 2H₂O, the coefficients show that 2 moles of hydrogen react with 1 mole of oxygen to form 2 moles of water. Therefore, the equation must include the coefficients needed to balance it; states of matter and whether the reaction is reversible are not required for basic stoichiometric calculations.

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