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.
