Balancing equations for chemistry? HELP!!?

Question

i can't figure out how to do this. one example is

C3 H8+ O2 -----> CO2 + H20

ok so the answer is C3 H8+ 5O2 ---> 3C02+ 4H2O

but how do you come up with that answer?

thanks!

Answer 1

You have 3 carbons on the left side, so you have to make 3 on the right side.

Then you have: C3 H8 + O2 ----> 3CO2 + H2O

After that, notice that you have 8 hydrogens on the left side and two on the right. So to make it balanced, you multiply by 4.

Then you have: C3 H8 + O2 ----> 3CO2 + 4H2O

Last, you notice you have 2 oxygens on the left, and ten on the right.

(6 from the CO2, because you distribute the 3...and 4 from the H2O).

So, to make ten oxygens on the left, put a 5.

C3 H8 + 5O2 ----> 3CO2 + 4H2O