Determine how many moles of O2 are required to react completely with 4.9 mol of C4H10

Answer 1

The first step in any stoichiometry problem is always a balanced equation. Oxygen + a hydrocarbon is a combustion reaction, so the products are going to be CO₂ and water.

C₄H₁₀ + O₂ = CO₂ + H₂O

Now this reaction isn't balanced. On the reactant side we have 4 C, 10 H, and 2 O, while the products have 1 C, 3 O, and 2 H. How to balance this out? Always start balancing a combustion reaction by balancing the carbons:

C₄H₁₀ + O₂ = 4CO₂ + H₂O

So now our reactant side is unchanged (4 C, 10 H, 2 O) but our product side is now 4C, 9O, and 2H. Our carbons match. Progress! Next do the same with the hydrogens, and then visit oxygen last. C → H → O is always a smart way to balance a combustion reaction.

Once you have the balanced reaction, the next step is to use dimensional analysis. We know we are beginning with 4.9 mol of C₄H₁₀, and what we are trying to figure out moles of O₂. The balanced equation can give us the ratio of (mol C₄H₁₀)/(mol O₂). Une dimensional analysis to make sure that we have mol C₄H₁₀ on both the top and the bottom, and mol O₂ on the top. That way mol C₄H₁₀ will cancel, and we'll be left with mol O₂ and our answer.

And don't forget to watch your sig figs!