rules for balancing redox equations

1. Assign oxidation numbers to every atom in the unbalanced chemical equation
2. Decide which species is being oxidized and which species is being reduced (remember: "OIL RIG")
3. Break the equation down into oxidation and reduction half-reations; remember that electrons appear as products in oxidation half-reactions and as reactants in reduction half-reactions
4. Balance the half-reactions so that when added together the electrons will cancel each other out
5. The equation must be balanced both with respect to mass and charge to be correct

practice problems

1. Fe₂O_{3 (s)} + CO_(g) => Fe_(s) + CO_{2 (g)}
2. Cu_(s) + NO₃^-_(aq) + H⁺_(aq) => Cu²⁺_(aq) + NO_{2 (g)} + H₂O _(l)
3. K_(s) + H₂O_(l) => KOH_(aq) + H_{2 (g)}
4. Zn_(s) + HBr_(aq) => ZnBr_{2 (aq)} + H_{2 (g)}
5. CuS_(s) + NO₃^-_(aq) + H⁺_(aq) => Cu²⁺_(aq) + SO₄^2-_(aq) + NO_(g)+ H₂O _(l)
6. Cl_{2 (g)} + NaI_(aq) => I_{2 (s)} + NaCl_(aq)
7. Cu(OH)_{2 (s)} + HNO_{3 (aq)} => Cu(NO₃)_{2 (aq)} + H₂O _(l)
8. F_{2 (g)} + H₂O_(l) => HF_(aq) + O_{2 (g)}
9. Cl_{2 (g)} + NaOH_(aq) => NaCl_(aq) + NaClO_(aq) + H₂O_(l)
10. H₂S_(g) + SO_{2 (g)} => S_(s) + H₂O_(l)

answers

1. Fe₂O_{3 (s)} + 3 CO_(g) => 2 Fe_(s) + 3 CO_{2 (g)}
2. Cu_(s) + 2 NO₃^-_(aq) + 4 H⁺_(aq) => Cu²⁺_(aq) + 2 NO_{2 (g)} + 2 H₂O _(l)
3. 2 K_(s) + 2 H₂O_(l) => 2 KOH_(aq) + H_{2 (g)}
4. Zn_(s) + 2 HBr_(aq) => ZnBr_{2 (aq)} + H_{2 (g)}
5. 3 CuS_(s) + 8 NO₃^-_(aq) + 8 H⁺_(aq) => 3 Cu²⁺_(aq) + 3 SO₄^2-_(aq) + 8 NO_(g)+ 12 H₂O _(l)
6. Cl_{2 (g)} + 2 NaI_(aq) => I_{2 (s)} + 2 NaCl_(aq)
7. Cu(OH)_{2 (s)} + 2 HNO_{3 (aq)} => Cu(NO₃)_{2 (aq)} + 2 H₂O _(l)
8. 2 F_{2 (g)} + 2 H₂O_(l) => 4 HF_(aq) + O_{2 (g)}
9. Cl_{2 (g)} + 2 NaOH_(aq) => NaCl_(aq) + NaClO_(aq) + H₂O_(l)
10. 2 H₂S_(g) + SO_{2 (g)} => 3S_(s) + 2 H₂O_(l)