Question

Balance
C3H6 + O2 > H2O + CO2

Answer 1

obviously, each C3H6 will produce 3CO2

so, start out with that:

C3H6 + O2 > H2O + 3CO2

Now, each C3H6 will generate 3H2, so we have

C3H6 + O2 > 3H2O + 3CO2

Now we have 3C and 6H on each side, but 9O on the right. Since O comes only in pairs on the left, we need to double things up:

2C3H6 + ?O2 > 6H2O + 6CO2

Now we are ready to finish up. O is independent of the other stuff on the left, so as long as the C and H balance, we can make O do so as well:

2C3H6 + 9O2 > 6H2O + 6CO2