What is an example of a balancing chemical equations practice problem?
Balance the equation for the combustion of heptane: C₇H₁₆ + O₂ → CO₂ + H₂O.
Start with the unbalanced equation:
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.
We start with
1 C₇H₁₆ + O₂ → CO₂ + H₂O
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
We can't balance O yet, because we have two formulas that contain O and lack coefficients. So we balance H instead.
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.
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.