Fe₂O₃ + CO -> Fe₃O₄ + CO₂ ----- 3 Fe₂O₃ + CO -> 2 Fe₃O₄ + CO₂

Fe₃O₄ + CO -> FeO + CO₂ ----- Fe₃O₄ + CO -> 3 FeO + CO₂

Ca + H₂O -> Ca(OH)₂ + H₂ ------ Ca + 2 H₂O -> Ca(OH)₂ + H₂

CaCl₂ + AgNO₃ ----> AgCl + Ca(NO₃)_{2 --------} CaCl₂ + 2 AgNO₃ ----> 2 AgCl + Ca(NO₃)₂

H₂SO₄ + NaOH ----> H₂O + Na_{2SO4 -----H2SO4 + 2NaOH ----> 2H2O + Na2SO4}