Calculate the mass of octane needed to release 6.20 mol co2

The combustion reaction of octane is as follow,

                           C₈H₁₈  +  25/2 O₂     →     8 CO₂  +  9 H₂O

According to balance equation,

8 moles of CO₂ are released when  =  114.23 g (1 mole) Octane is reacted

So,

      6.20 moles of CO₂ will release when  =  X g of Octane is reacted

Solving for X,
                                     X  =  (114.23 g × 6.20 mol) ÷ 8 mol

                                     X  =  88.52 g of Octane
Result:
           88.52 g of Octane is needed to release 6.20 mol CO₂.