Question

As with any combustion reaction, the products of combusting a hydrocarbon fuel (CxHy) with oxygen (O2) are carbon dioxide (CO2) and water (H2O).
A mass of 16.74 g for an unknown fuel was combusted in a reaction vessel containing an unknown amount of oxygen. At the end of the reaction, there still remained 16.70 g of the fuel as well as 0.0654 g of water and 0.1198 g of carbon dioxide. The oxygen was completely consumed during the reaction.

How many molecules of oxygen gas were initially present in the reaction vessel?


Please help me, I will be very thankful. The topic is limiting reagents and theoretical yields.

Answer 1

Answer:

5 molecules of oxygen will be present

Explanation:

In this reaction combustion is taking place hence there must be presence of oxygen in it.

We don't know the initial amount of carbon molecules in hydrogen molecules present hence the equation goes:-

$CxHy + O_2 => CO_2+ H_2O$

Mass of  fuel 16.74 grams, Mass of carbon dioxide is 1198 gram and water is 0.0654 remaining mass of  fuel is 16.70 g.  Hence amount of fuel used up is 0.04 gram  

$0.04 + O => 0.1198 + 0.0654$

Weight of products is 0.1852 and weight of oxygen is 0.1452

No of molecules will be $\frac {(0.1452 \times 6.023 \times 10^-^2^3)}{ (1.661 \times 10^-^2^4)} = 5$molecules