Balancing Equations Worksheet with Key for chemistry practice.

1. a) Reactants: 2 H₂ and O₂
b) Product: 2 H₂O
c) Coefficient "2" in front of H₂ means two molecules of hydrogen gas.
d) Yes, the reaction is balanced because the number of atoms of each element is equal on both sides (4 H and 2 O).
e) A coefficient is needed for O₂ to balance the oxygen atoms; without it, there would be only 2 oxygen atoms on the left but 4 on the right.
f) Four hydrogen atoms are needed to produce two H₂O molecules.
g) Two oxygen atoms are needed to produce two H₂O molecules.
h) Two oxygen atoms are needed to produce one H₂O molecule.
i) The word equation is: Hydrogen gas reacts with oxygen gas to produce water.

2. a) 4 Fe + 3 O₂ → 2 Fe₂O₃
b) H₂ + Cl₂ → 2 HCl
c) 2 Ag + H₂S → Ag₂S + H₂
d) CH₄ + 2 O₂ → CO₂ + 2 H₂O
e) HgO → Hg + ½ O₂ (or 2 HgO → 2 Hg + O₂)
f) CO + 3 H₂ → CH₄ + H₂O

3. a) 2 Al + 3 CuBr₂ → 2 AlBr₃ + 3 Cu
b) 2 LiBr + Na₂SO₄ → Li₂SO₄ + 2 NaBr
c) 2 Zn + O₂ → 2 ZnO