Question Video: Deducing the Molar Ratio of Reactants from a Balanced Reaction Equation Chemistry

Methane burns in oxygen according to the following equation: CH₄ + 2O₂ ⟶ CO₂ + 2H₂O. a) What is the molar ratio of methane to oxygen? b) What is the molar ratio of methane to carbon dioxide? c) What is the molar ratio of oxygen to water?

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Video Transcript

Methane burns in oxygen according to the following equation: CH4 plus 2O2 reacts to form CO2 plus 2H2O. What is the molar ratio of methane to oxygen?

This question is asking us to create molar ratios, which are ratios that help us relate amounts of different chemical species that are participating in the same chemical reaction. Molar ratios are useful to us because they help us convert between amounts of one substance and amounts of another. To create molar ratios, we’ll use the stoichiometric coefficients from a balanced chemical equation, which refer to the amount of each chemical species that participates in the reaction in moles.

So before we create our molar ratios, let’s quickly ensure that our chemical equation is balanced. There is one carbon on each side of the equation, four hydrogens, and four oxygens. So our equation is balanced and good to go. This question is asking us to create a molar ratio between methane and oxygen. And as we can see from looking at our balanced chemical equation, the stoichiometric coefficient in front of methane is one and the stoichiometric coefficient in front of oxygen is two. So the molar ratio of methane to oxygen is one to two, which means that for every one mole of methane, two moles of oxygen is needed to react with it.

What is the molar ratio of methane to carbon dioxide?

Now, we want to do the same thing, but for a ratio of methane to carbon dioxide. As we can see from our balanced chemical equation, we need one mole of methane to produce one mole of carbon dioxide, which gives us a molar ratio of one to one.

What is the molar ratio of oxygen to water?

Now, we need the ratio of O2 to H2O. The stoichiometric coefficients in front of both oxygen and water are two. So we get a ratio of two to two. But you’ll notice that we can simplify this ratio by dividing it by two, which would give us a ratio of one to one, which is the correct molar ratio, as we should always express these molar ratios in the simplest whole numbers that we can. So the molar ratio of oxygen to water is one to one.

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