Write a balance equation for the combustion of isoprene, C5H8, in an abundant supply of oxygen?

2 Answers
Mar 31, 2015

#C_5H_8+7O_2rarr5CO_2+4H_2O#

It helps if you leave the oxygen last when you balance it.

Mar 31, 2015

Michael's answer is perfectly correct. Here's how you get it.

The combustion of a hydrocarbon forms carbon dioxide and water.

So the unbalanced equation is

C₅H₈ + O₂ → CO₂ + H₂O

The procedure is called balancing by inspection.

Let's start with the most complicated formula, C₅H₈. We put a 1 in front of it.

#color(red)(1)"C₅H₈" + "O₂" → "CO₂" + "H₂O"#

We have fixed 5 C atoms on the left, so we need 5 C atoms on the right. We put a 5 in front of CO₂.

#color(red)(1)"C₅H₈" + "O₂" → color(green)(5)"CO₂" + "H₂O"#

We have also fixed 8 H atoms in the C₅H₈, so we need 8 H atoms on the right. We put a 4 in front of the H₂O.

#color(red)(1)"C₅H₈" + "O₂" → color(teal)(5)"CO₂" + color(blue)(4)"H₂O"#

Now we have fixed 14 O atoms on the right, so we need 14 O atoms on the left. We put a 7 in front of the O₂.

#color(red)(1)"C₅H₈" + color(orange)(7)"O₂" → color(teal)(5)"CO₂" + color(blue)(4)"H₂O"#

The equation should now be balanced. Let's check.

On the left: 5 C; 8 H; 14 O
On the right: 5 C; 14 O; 8 H

It's balanced.