In the combustion of octane, how many grams of oxygen are needed to completely react and produce 84.00 grams of carbon dioxide?

95.4g

Explanation:

Given parameters:

Mass of carbon dioxide = 84g

Unknown:

Mass of oxygen = ?

Solution:

To solve this problem, we will simply work backward from the known to the unknown specie.

We first must write the balanced equation of the reaction;

             2C₈H₁₈   +    25O₂      →       16CO₂     +      18H₂O

Now, convert the mass of CO₂ to number of moles;

         Number of moles  =

              Molar mass of CO₂ = 12 + 2(16) = 44g/mol

        Number of moles  =   = 1.91moles

From the balanced equation,

                   16 moles of CO₂ is produced by 25 moles of O₂

                   1.91 mole of CO₂ will be produced by   = 2.98mole of O₂

Now, we convert this moles of Oxygen gas to mass;

     Mass of O₂  = number of moles x molar mass

                           = 2.98 x 2(16)

                            = 95.4g

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