Write the balanced equation for the complete combustion of hexene (C6H12)

The easiest way to balance any combustion equation is to
first write the general form.  In a combustion reaction the products are always carbon
dioxide (CO2) and water (HOH) and the reactants are the organic material plus oxygen
(O2).

General Form:

C6H6 +  O2
-->   CO2  +  HOH

Now start by balancing the carbon
atoms:

six carbons on the left so you need 6 on the
right.

C6H6   +   O2   --->    6 CO2  + 
HOH

Next balance the hydrogen
atoms:

6 on the left, so you need 6 on the
right.

C6H6  +   O2 -->   6 CO2    +   3 
HOH

Now count the number of oxygen on the right = 12 + 3 =
15

divide the number on the right by 2 to get the number
needed on the left.   15/2 = 7.5

C6H6  +  7.5  O2
-->  6 CO2  +  3 HOH

But the rule is that
coefficients have to be whole numbers.  So multiple both sides by 2 to get the final
balanced equation.

2 C6H6 + 15  O2  -->  12 CO2   +
6 HOH

To be sure, count the number of each element on each
side:

On the left you have 12 C, 12 H, 30
O

On the right you have 12 C, 12 H, 30 O so it is
balanced.