Ca + 2HCl = CaCl2 + H2
Ca + 2H2O = Ca(OH)2 + H2
Ca + S = CaS
Ca + Cl2 = CaCl2
Ca + F2 = CaF2
Ca + Br2 = CaBr2
Ca + I2 = CaI2
S -> SO2 -> SO3 -> H2SO4 -> BaSO4
1. S + O2 = SO2
2. 2SO2 + O2 = 2SO3
3. SO3 + H2O = H2SO4
4. H2SO4 + BaCl2 = BaSO4 + 2HCl
Zn -> ZnO -> ZnCl2 -> Zn(OH)2 -> ZnO
1. 2Zn + O2 = 2ZnO
2. ZnO + 2HCl = ZnCl2 + H2O
3. ZnCl2 + 2NaOH = Zn(OH)2 + 2NaCl
4. Zn(OH)2 = ZnO + H2O