Question

Which is the balanced chemical equation representing the decomposition of hydrogen peroxide? H2O2 H2O + O2

Answer 1

2H2O2 ------> 2H2O +O2

because we're given one side with 2 hydrogens and 2 oxygens and another sie with  3 oxygens and 2 hydrogens. The hydrogens are balanced but the oxygens are not. You can't make the oxygen a three on the reactants side with a whole number so you multiply by 2. 

Now you have 4 hydrogens and 4 oxygens on one side and 4 hydrogens and 4 oxygens on the other :)