Answer:
1 C3H8 + 5 O2 --> 3 CO2 + 4 H2O
Explanation:
USE PENCIL! Balancing equations typically requires some initial trial and error. Making changes is common.
_ C3H8 __ O2 --> __ CO2 __ H2O
We know we can only have whole molecules, so all number coefficients must be, eventually, whole numbers. It is OK to start with a fraction, but the final must be a shole number. Pick the most complex molecule (either product or reactant) and assign it a coefficient of 1.
1 C3H8 __ O2 --> __ CO2 __ H2O
Now find places for each of the atoms in C3H8 on the product side. 3 carbons means we need 3CO2 molecules, so add a coeffient of 3,
1 C3H8 __ O2 --> 3 CO2 __ H2O
3 CO2 means we need 6 oxygens, so add a coefficient of 3 for the O2:
1 C3H8 + 3 O2 --> 3 CO2 __ H2O
Now find a home for the 8 hydrogens that come from the 1 C3H8. Add 4 to the H2O product:
1 C3H8 + 3 O2 --> 3 CO2 + 4 H2O
This last step added 4 more O to the product side, so we need to adjust the reactant source of O:
1 C3H8 + 5 O2 --> 3 CO2 + 4 H2O
Double check the result:
Element Reactant Product
C 3 3
H 8 8
O 10 10(6+4)
Everything checks.
[Note that one might use a fraction such as 1/2 or 1/3 just to make the balance work. But fractions must be converted to whole numbers for the final equation. For 1/2, multiply all coefficients by 2. By 3 for 1/3, etc.]
