# 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?

##### 1 Answer

#### Explanation:

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.

where

Then the first side

solving n

Then the formula is

Now, the same result should be obtained from the other side, lets try it out.