How to balance a chemical equation.

Balancing chemical equations can seem tricky at first, especially when starting out. But by following an order it becomes a quick and easy task.

For the sake of this question we'll balance this equation:
C5H12 + O2 → CO2 + H2O

It's easiest to start from left to right and work your way along until the equation is balanced, then any cancellation can be done.

1. C5H12 + O2 → CO2 + H2O

We can see there are 5 carbons on the left and only 1 on the right, so balance the carbons first

C5H12 + O2 → 5CO2 + H2O

2. C5H12 + O2 → 5CO2 + H2O

There are 12 hydrogens on the left but only 2 on the right, so multiply by 6 to balance.

C5H12 + O2 → 5CO2 + 6H2O

3. C5H12 + O2 → 5CO2 + 6H2O

Now the right hand side has much more oxygens than the left, 10 from the 5COand 6 from the 6H2O for a total of 16. So multiply the O2 on the left by 8 to get 16.

C5H12 + 8O2 → 5CO2 + H2O.

And there you go, the equation is balanced. Working systematically works for even complicated equations.

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