How many moles of CO2 will be produced from 72G of CH4 assuming O2 is available in excess

Answer 1

First you need to realize that this is a stoichiometry problem that requires a balanced chemical equation. Since CO₂ is produced from CH₄ and O₂, this will be a combustion reaction with water as the other product.

The equation should look like this: CH₄ + O₂ → CO₂ + H₂O

and balanced it should look like this: CH₄ + 2 O₂ → CO₂ + 2 H₂O

Now we can start the stoichiometry! Stoichiometry is a mole-mole ratio of two or more species in a balanced chemical reaction. It allows you to convert the moles of one species to the moles of another. Since the problem gives you the mass of methane, the first stoichiometry step is to convert it to moles, then you can look at the mole-mole ratio.

The first step should look like this:

72 g CH₄ x 1 mol CH₄ / 16 g CH₄ = 4.5 mol CH₄

The next step is to convert the moles of CH₄ to moles of CO₂:

4.5 mol CH₄ x 1 mol CO₂ / 1 mol CH₄ = 4.5 mol CO₂

In that mole-mole step I used 1 mole for CO₂ and 1 mole for CH₄ because there was no number in front of CO₂ or the CH₄ in the balanced equation, which is the same as a 1. You may be tempted to skip this step because the 1's cancel out, but DON'T DO IT! That step is the most important step of stoichiometry and just because it coincidentally turned out not to matter to this problem, it likely will matter in the next problem and it is good to remember that this step exists.

If you put both steps together, you have a stoichiometry problem:

72 g CH₄ x 1 mol CH₄ / 16 g CH₄ x 1 mol CO₂ / 1 mol CH₄ = 4.5 mol CO₂

The answer is 4.5 mol CO₂

Answer 2

The first step is balancing the reaction. The reactants are CH4 and O2 and the products will be CO2 and H2O.

The balanced equation looks like this:

CH4 + O2 --> CO2 + 2H2O

Since the coefficients of CH4 and CO2 are both 1, it means that every one mole of CH4 consumed, one mole of CO2 is produced.

Next we convert 72 grams of CH4 to moles. From the periodic table you can calculate that one mole of CH4 has a mass of 16 grams (Carbon has a mass of 12 and each Hydrogen has a mass of 1).

Take the total mass (72) and divide by the molar mass (16) and you will calculate the moles of CH4, which is 4.5. Since each mole of CH4 consumed produces one mole of CO2, you can say that you will produce 4.5 moles of CO2.