The equation 2C8H8 + 25O2 → 8CO2 +18H2O is not completely balanced.
Explanation
The equation above does not obey the law of mass conversation which state that the mass in isolated system is neither created nor destroyed in a chemical reaction. This mean that the mass of the product must be equal to the mass of reactant.
In the equation above the total mass of reactant is 2+25= 27
while mass of the product = 8+18= 26 thus the equation is not balanced