# What is an example of a balancing chemical equations practice problem?

Jun 20, 2014

Balance the equation for the combustion of heptane: C₇H₁₆ + O₂ → CO₂ + H₂O.

C₇H₁₆ + O₂ → CO₂ + H₂O

A method that often works is to balance everything other than O and H first, then balance O, and finally balance H.

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

The most complicated formula looks like C₇H₁₆. We put a 1 in front of it to remind ourselves that the coefficient is now fixed.

1 C₇H₁₆ + O₂ → CO₂ + H₂O

Balance C:

We have fixed 7 C atoms on the left hand side, so we need 7 C atoms on the right hand side. We put a 7 in front of the CO₂.

1 C₇H₁₆ + O₂ → 7 CO₂ + H₂O

Balance O:

We can't balance O yet, because we have two formulas that contain O and lack coefficients. So we balance H instead.

Balance H:

We have fixed 16 H atoms on the left hand side, so we need 16 H atoms on the right hand side. We put an 8 in front of the H₂O.

Now we can balance O:

We have fixed 22 O atoms on the right hand side: 14 from the CO₂ and 8 from the H₂O. We put an 11 in front of the O₂.

1 C₇H₁₆ + 11 O₂ → 7 CO₂ + 8 H₂O

Every formula now has a fixed coefficient. We should have a balanced equation.

Let’s check:

Left hand side: 7 C, 16 H, 22 O
Right hand side: 7 C, 22 O, 16 H

All atoms balance. The balanced equation is

C₇H₁₆ + 11O₂ → 7CO₂ + 8H₂O

Hope this helps.