# What is the balanced equation of SO2 + O2 = SO3?

May 26, 2014

The balanced equation is ${\text{2SO"_2 + "O"_2 → "2SO}}_{3}$.

#### Explanation:

You follow a systematic procedure to balance the equation.

${\text{SO"_2 + "O"_2 → "SO}}_{3}$

A method that often works is to balance everything other than $\text{O}$ and $\text{H}$ first, then balance $\text{O}$, and finally balance $\text{H}$.

Another useful procedure is to start with what looks like the most complicated formula.

The most complicated formula looks like ${\text{SO}}_{3}$. We put a 1 in front of it to remind ourselves that the number is now fixed.

${\text{SO"_2 + "O"_2 → color(red)(1) "SO}}_{3}$

Balance $\text{S}$:

We have $\text{1 S}$ on the right, so we need $\text{1 S}$ on the left. We put a 1 in front of the ${\text{SO}}_{2}$.

$\textcolor{b l u e}{1} {\text{SO"_2 + "O"_2 → color(red)(1) "SO}}_{3}$

Balance $\text{O}$:

We have $\text{3 O}$ on the right, so we need $\text{3 O}$ on the left. There are already $\text{4 O}$ atoms on the left. We must put a ½ in front of the ${\text{O}}_{2}$.

Most instructors don't allow fractions in balanced chemical equations, because you can't have a fraction of an atom or a molecule.

To get rid of the fractions, you multiply all the coefficients by 2 and get

$\textcolor{b l u e}{2} {\text{SO"_2 + "O"_2 → color(red)(2) "SO}}_{3}$

Now you can balance the equation by putting a 1 in front of the ${\text{O}}_{2}$.

$\textcolor{b l u e}{2} {\text{SO"_2 + color(orange)(1) "O"_2 → color(red)(1) "SO}}_{3}$

We should now have a balanced equation.

Check to make sure:

$\boldsymbol{\text{Atom"color(white)(m)bb "Left hand side"color(white)(m) bb"Right hand side}}$
stackrel(————————————————)(color(white)(ml)"S"color(white)(mmmmmm) 2color(white)(mmmmmmmll) 2)
$\textcolor{w h i t e}{m l} \text{O} \textcolor{w h i t e}{m m m m m l l} 6 \textcolor{w h i t e}{m m m m m m m l l} 6$

The balanced equation is

${\text{2SO"_2 + "O"_2 → "2SO}}_{3}$