Year 9 Chemical Reactions: Properties, Equations, and Energy Changes Practice Test

Balancing decomposition to water and oxygen means conserving every atom on both sides. Hydrogen peroxide breaks down into water and oxygen gas, and a catalyst simply speeds that up without changing the amounts.

Left side has 2 H2O2, which gives 4 hydrogen atoms and 4 oxygen atoms. To match the 4 hydrogens on the right, you need 2 H2O, which supplies 4 hydrogens but only 2 oxygens. To balance the total oxygen atoms, you add O2 on the right, which provides the remaining 2 oxygens. Now the right side has 2 H2O (4 H, 2 O) plus O2 (2 O), totaling 4 O and 4 H, matching the left.

Thus the balanced equation is 2 H2O2 -> 2 H2O + O2. Writing a single H2O2 would require a fractional amount of O2 to balance, which isn’t used in whole-number equations. Also, producing atomic oxygen (O) isn’t the typical product form in such reactions.