Question

How do you write a balanced chemical equation for the combustion of `C_2H_2`?

Answer 1

Complete combustion of hydrocarbons ALWAYS results in the formation of carbon dioxide and water:

`"Hydrocarbon + dioxygen " rarr" carbon dioxide + water"`

Explanation:

And when we combust a hydrocarbon, to represent the equation, typically we would balance the carbons, and then the hydrogens, and then the oxygens......so..........

`C_2H_2 rarr 2CO_2`, carbons are balanced;

`HC-=CH rarr 2CO_2 + H_2O`, hydrogens are balanced;

And now balance the equation with respect to oxygens;

`HC-=CH(g) +3/2O_2(g)rarr2CO_2(g) + H_2O(g)`

If you like, you can double the entire equation to get rid of the half-integral coefficient. The arithmetic is generally easier if you use it in the given form. The use of half-integral coefficients for binuclear molecules has long precedent.

Can you likewise represent complete combustion of `"ethylene"`, `H_2C=CH_2`; what about `"ethane"`, `H_3C-CH_3`? How does energy transfer in these combustion equations?