# What happens in a combustion reaction?

Jul 27, 2018

A material, a fuel, is oxidized by dioxygen gas....

#### Explanation:

And typically an hydrocarbon fuel is completely combusted to give carbon dioxide and water...and ENERGY....

As we examples, we consider the COMPLETE combustion of propane, and butane gases. The usual rigmarole is balance the carbons, as carbon dioxide....

$\left(i\right)$ ${\underbrace{{C}_{3} {H}_{8} + {O}_{2} \rightarrow 3 C {O}_{2} + {H}_{2} O}}_{\text{UNBALANCED}}$

Then balance the hydrogens, as water..........

$\left(i i\right)$ ${\underbrace{{C}_{3} {H}_{8} + {O}_{2} \rightarrow 3 C {O}_{2} + 4 {H}_{2} O}}_{\text{UNBALANCED}}$

Then, finally, balance the oxygens....

$\left(i i i\right)$ ${\underbrace{{C}_{3} {H}_{8} + 5 {O}_{2} \rightarrow 3 C {O}_{2} + 4 {H}_{2} O}}_{\text{BALANCED}}$

With even-numbered alkanes, to achieve stoichiometric equivalence you have to either double the entire equation, or use a a half-integral coefficient, i.e. for butane.....

${C}_{4} {H}_{10} \left(g\right) + \frac{13}{2} {O}_{2} \left(g\right) \rightarrow 4 C {O}_{2} \left(g\right) + 5 {H}_{2} O \left(l\right)$

$2 {C}_{4} {H}_{10} \left(g\right) + 13 {O}_{2} \left(g\right) \rightarrow 8 C {O}_{2} \left(g\right) + 10 {H}_{2} O \left(l\right)$

Would energy be released or absorbed in these reactions? Why?