Answer
$2CH=CH $+ $5O_{2}$ --> $4CO_{2}$ + $2H_{2}O$
Work Step by Step
Hydrocarbons undergo a combustion reaction, Carbon dioxide and water are given off as the end products of the reaction.
If we try to balance this equation directly, we get 5 oxygen atoms on the right-hand side, which means we need to put 2.5 in front of oxygen. 2.5 $\times$2=5
Therefore to get a whole number we balance it by adding 2 in front of the alkyne. Thus,
1. There are 4 Carbon atoms on the left-hand side which gets balanced when we balance carbon dioxide with a 4.
$2CH=CH $ --> $4CO_{2}$
2. There are 4 hydrogen atoms on the left-hand side which gets balanced when we place 2 in front of a water molecule. (2$\times$2= 4).
$2CH=CH $ --> $2H_{2}O$
3. There are 10 oxygen atoms on the right-hand side. 4$\times$2= 8+2=10
These get balanced when we place 5 in front of an oxygen molecule on the left-hand side. (5$\times$2=10)
$2CH=CH $+ $5O_{2}$ --> $4CO_{2}$ + $2H_{2}O$
