well , first you write the formulas of the reactants and the reaction products. and then you balance the equation, making sure the number of atoms of each substance that appear among the reactants is the same that is in the reaction products.
here it goes..
Hydrogen plus Oxygen yield water.
2H2+ O2--> 2H2O
Nitrogen plus hydrogen yield ammonia.
N2+2H2-->2NH4
Aluminum bromide plus chlorine yield aluminum chloride and bromine.
2AlBr3+ 3Cl2--> 2AlCl3+3Br2
Hydrochloric acid plus sodium hydroxide yield sodium chloride plus water.
HCl+NaOH-->NaCl+H2O
Iron plus Lead(2) sulfate react forming iron(2) sulfate plus lead.
Fe+ PbSO2-->FeSO2+2Pb
Potassium chlorate when heated produces potassium chloride plus oxygen gas.
KClO3---> KCl+ 3/2O2
Sulfuric acid decomposes to form sulfur trioxide gas plus water.
H2SO4-->SO3+H2O
Sodium oxide combines with water to make sodium hydroxide.
Na2O+H2O-->2NaOH
Potassium iodide reacts with bromine forming potassium bromide plus
2KI+ BR2--> 2KBr+ I2