Which one of the following equations is not balanced?

6H2O + 6CO2 - - - > C6H12O6 + 6O2

C7H16 + 11O2 - - - > 7CO2 + 8H2O

PCl2 + 4H2O - - - >H3PO4 + 5HCL

Fe3O4 + 4H2 - - - > 3Fe + 4H2O

The key in the balancing of chemical reaction is to make sure that you got the exact chemical formula of the substance that is reacting and the yielded product. After getting the formula, identify first the hardest element/atom to be balanced such as Na, Zn, Cl, C, O, etc. Then proceed to the easier ones such as O, H. Make sure to note the atoms present in the molecule of the substance. Among the three equations, PCl2 + 4H2O - - - >H3PO4 + 5HCL is not balanced. The hardest element here is the Cl. Observe that there are 5Cls in the product side so you must add 5 to the PCl2. However, there are only 2Cl atoms and it needs 3 to balance the equation. Also, there is no P in the product side. This equation is invalid.

The third one is incorrectly balance because the are only two chlorine on the reactant side and five on the product side. The correct balanced equation is 2PCL2 + 8H2O - > 2H3PO4 + 5H2 + 4Cl. The reason HCl is broken into two parts is because it is a strong acid and would immediately dissolve if put together.