Chemistry 101 - Reactions

Question

You burn a gasoline (C₈H₁₈) in the presence of oxygen, producing carbon dioxide and water vapor. If the gasoline weighed 137.4 g and the masses of carbon dioxide and water vapor produced were 424.3 g and 195.3 g respectively, what mass of oxygen gas was consumed? (Assume there were no other reactants of products). 

Answer 1

Let's look at the balanced equation for the reaction taking place:

2C₈H₁₈ + 25O₂ ==> 16CO₂ + 18H₂O ... balanced equation for combustion of octane (C₈H₁₈)

We know we obtained 424.3 g CO₂ and195.3 g of H₂O. We know we started with 137.4 g of C₈H₈. By the law of conservation of mass, we can find the mass of O₂ used. Assuming no losses, the mass of the reactants must equal the mass of the products

424.3 g + 195.3 g = 619.6 g total mass of products

619.6 g - 137.4 g = 482.2 g O₂ used