Cecil writes the equation for the reaction of hydrogen and oxygen below.H2 + O2 → H2O

A chemical equation represents the substances before and after a reaction, and balancing it ensures the same number of each type of atom appears on both sides. For example, the balanced equation is 2H₂ + O₂ → 2H₂O: there are 4 hydrogen atoms and 2 oxygen atoms on each side. This shows that atoms are conserved in chemical reactions, not created.

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