The combustion of a gaseous alkane produces 7 L of carbon dioxide plus water vapour. If the original volume of alkane plus oxygen was 6 L, what is the formula of the alkane?
The reaction used is a normal total oxidation of the hydrocarbon by oxygen:
The coefficient for the O_2 is coming from the addition of the ones for the products.
Using the ideal gas formula PV=nRT, where everything is constant but V and n, we can relate both states, before and after the reaction.
Then the first side
Then the formula is
Now, the same result should be obtained from the other side, lets try it out.