To determine the moles of O₂ needed, we have to know in what ratio the two reactants react and then use the moles of C₂H₂ in reaction to determine the moles of O₂ needed. We can find this out based on their coefficient in a balanced equation:
Write a Balance Equation
2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O
Compare the Mole Ratio (Equation Coefficient of C₂H₂ to O₂)
Based on the equation, the mole ratio of C₂H₂ to O₂ is 2 to 5. Therefore for every molecule of C₂H₂, ⁵/₂ C₂H₂ molecules are needed to react.
Find the moles of O₂
Since the number of moles of C₂H₂ = 2.60 moles
then moles of O₂ = 2.60 moles × ⁵/₂
