# What is an example of an stoichiometry practice problem?

Sep 24, 2015

For A2 level:

Diesel (${C}_{10} {H}_{22}$) is a commonly used fuel for trucks and cars.

$1.$ Represent the complete combustion of diesel fuel to $C {O}_{2}$ and water.
$2.$ If 1 kg of diesel is combusted, what is (i) the mass, and (ii) the volume at SLC, of carbon dioxide produced.

#### Explanation:

$1.$ Stoichiometry problems that feature combustion of hydrocarbons are very topical and popular. This question requires a balanced chemical equation, and then some calculations.

${C}_{10} {H}_{22} \left(l\right) + \frac{31}{2} {O}_{2} \left(g\right) \rightarrow 10 C {O}_{2} \left(g\right) + 11 {H}_{2} O \left(l\right)$

We assume standard conditions, and we ensure that the equation is stoichiometric, i.e. precisely balanced; is it? If we use a ${C}_{10}$ hydrocarbon, then complete combustion requires $10$ equiv of $C {O}_{2}$. Hydrogen is oxidized to water, hence $11$ equiv water result. To balance the oxygen, I have a 1/2 equiv quantity of oxygen gas (I could remove this how?)

$2.$ We have a limited amount of diesel fuel and and we must calculate the the mass of the carbon dioxide produced. We must also calculate the volume of gas produced given that 1 mol of gas (whose behaviour is reasonably idealized) occupies $24.5$ ${\mathrm{dm}}^{3}$ under SLC.

I have done a bit of spoonfeeding here, in that I gave you the chemical equation. You would be required to reproduce this at A level. A more advanced question would introduce more realistic conditions. Some of the hydrocarbon would be incompletely combusted to $C O$ and $C$. How could this be represented in the equation?