Chemistry => Chemical Reactions => Combustion Reaction
A combustion reaction like the one mentioned consists of oxidizing a fuel(CnHm) to obtain CO2 and Water.
We must take into account that during the chemical reaction there is breaking or formation of bonds, but the number of atoms is maintained.
The empirical formula is the simplest way to express a compound, it tells us the proportion in which the elements are in the molecule
To find the empirical formula we must find the number of moles of carbon and hydrogen produced, these moles will be equal to the moles in the reactants.
We will find the moles of the products from the reactants CO2 and Water, we must pass the mass they give us to moles. We have to divide the mass given between the molar mass of each compound.
Molar Mass H2O = 18.01g/mol
Molar Mass CO2 = 44.01 g/mol
Moles of H2O, atoms of H
In the H2O molecule, there are two hydrogen atoms, so the hydrogen atoms present in the products and reactants will be 0.15x2=0.30 H atoms
Moles of CO2, atoms of C
In the CO2 molecule, there is 1 carbon atom, so the carbon atoms present in the products and reactants will be 0.10 x 1 = 0.10 C atoms
We already know how many atoms of carbon and hydrogen we have. We have 0.10atoms of carbon and 0.30 atoms of H.
To find the empirical formula we divide the number of atoms between the smallest number of atoms found, that is, between 0.10. We will have:
So, the empirical formula will have 1 atom of carbon and 3 atoms of hydrogen, which means that the empirical formula will be: CH3
Answer: c. CH3