Write a balanced equation for the combustion of gaseous ethane (c2h6), a minority component of natural gas, in which it combines with gaseous oxygen to form gaseous carbon dioxide and gaseous water.

The original reaction equation is:
C2H6(g) + O2(g) → CO2 + H2O
but this is not a balanced equation, SO we have to compare the no of atoms on both sides:
1-C atoms: we have 2 atoms on the left side and 1 on the right side so we put 2CO2 instead of CO2
C2H6(g) + O2(g) → 2CO2(g) + H2O(g)
2- H atoms: we have 6 atoms on the left side and 2 atoms on the right side so we put 3H2O instead of H2O
C2H6(g) + O2(g) →2CO2(g) + 3H2O(g)
2- O atoms: we have 2 atoms on the left side and 7 atoms in left side so we put 7/2O2 instead of O2
C2H6(g) + 7/2 O2(g) → 2CO2(g) + 3H2O(g)  by dividing this equation by 2
∴the final balanced equation of our reaction is:
2C2H6(g) + 7 O2(g) → 4CO2(g) + 6 H2O(g)
as
C atoms on both sides = 4
H atoms on both sides = 12
O atoms on both sides = 14 

B. a graduated substance