Engineering Having trouble calculating the air supply necessary for combustion

[Remusco]

Homework Statement

Fuel is burned in a furnace with 12% excess air to minimize the formation of partially oxidized product. The average molecular weight of the fuel is 126. The overall complete stoichiometric combustion reaction is:

Relevant Equations

C_9H_18 + 13.5 O_2 +50.8 N_2 ---> 9CO_2 +9H_2O + 50.8N_2

I'm surprised that I'm getting this wrong. Seems like everything checks out in my calculation. Correct answer is supposedly C.

 

[mjc123]

Your mistake is in saying you have 13.5 moles of air. 1 mole of air is 0.2 mol O₂ + 0.8 mol N₂. Actually you have 13.5 moles O₂ and the stoichiometric amount of N₂.

 

[Remusco]

Your mistake is in saying you have 13.5 moles of air. 1 mole of air is 0.2 mol O₂ + 0.8 mol N₂. Actually you have 13.5 moles O₂ and the stoichiometric amount of N₂.

Makes sense. Thanks.