Please check if I've balance the equation correctly.

C8H18 + 25/2O2 --> 8CO2 + 9H2O

Generally assume that fractions are not allowed when balancing chemical equations.

There are a few exceptions, such as when the chemical equation is an intermediate step as part of a calculation, such as a thermochemical calculation as DrBob says. Another is where there is water of crystallization.

Outside of chemistry, biologists and earth scientists will use fractions and even decimals.

To check if an equation is balanced, we need to ensure that the number of atoms of each element is the same on both sides of the equation.

Let's break down the equation and count the number of atoms for each element on both sides:

On the left side:
- Carbon (C): 8 atoms
- Hydrogen (H): 18 atoms
- Oxygen (O): 25/2 atoms

On the right side:
- Carbon (C): 8 atoms
- Oxygen (O): 8 atoms (since there are 8 CO2 molecules, and each CO2 molecule contains 2 oxygen atoms)
- Hydrogen (H): 18 atoms (since there are 9 H2O molecules, and each H2O molecule contains 2 hydrogen atoms)

It appears that the equation is not balanced, specifically in terms of the oxygen atoms.

To balance the equation, we need to make the number of oxygen atoms the same on both sides. In this case, to do that, we can multiply the coefficient in front of the O2 molecule on the left side by 2:

C8H18 + 25/2 O2 --> 8CO2 + 9H2O

After multiplying by 2, the equation becomes:

C8H18 + 25 O2 --> 8CO2 + 9H2O

Now, let's count the number of atoms on each side again:

On the left side:
- Carbon (C): 8 atoms
- Hydrogen (H): 18 atoms
- Oxygen (O): 25 atoms

On the right side:
- Carbon (C): 8 atoms
- Oxygen (O): 8 atoms
- Hydrogen (H): 18 atoms

Now that the number of atoms of each element is the same on both sides, we can conclude that the equation is balanced.

It is balanced; however, some profs are not impressed with fractional numbers (but thermo profs always allow them).