Balancing of a chemical reaction by trial and error method, step 1. Write the chemical equation from the given word equation. For example, NaOH plus HCl gives N SCl plus H2O. It is derived from sodium hydroxide plus hydrochloric acid gives sodium chloride plus water. Step 2. Compare the number of atoms of various elements present on the two sides of the arrow, that is, of the equation. If it is the same, then the reaction is already balanced. On the reactant side, Na has 1 atom and on the product side, it also has 1 atom. On the reactant side, as well as the product side, O has 1 atom. H has 2 atoms, both on the reactant as well as product side. CL has 1 atom on the reactant side and 1 atom on the product side. Number of atoms of all the elements on the reactant and product side are same, so the reaction is balanced. ALCl3 plus H2O gives LOH thrice plus HCl. In this reaction, the total number of elements on both sides are unequal, so the reaction is unbalanced. AL has 1 atom on both sides. CL has 3 atoms on the reactant side, but only 1 on the product side. H has 2 atoms on the reactant side, but 4 atoms on the product side. O has 1 atom on the reactant side, but 3 atoms on the product side. Step 3. Start balancing an equation from the compound which contains maximum number of atoms. Moreover, it is convenient to consider, first that element in the same compound, which has unequal number of atoms on the two sides. Please remember that the formula of the compound must remain the same, while balancing the number of atoms. Select ALOH thrice for balancing. Number of AL on both sides are equal, so select oxygen for balancing next. Initially, in the reactants, the number of oxygen is 1 and the number of product is 3. So, to balance, we will multiply by 3 in the reactant side. So the formula of H2O cannot be changed to H2O3. Instead, a coefficient of 3 will have to be written before H2O. Such as ALCl3 plus 3H2O gives ALOH thrice plus HCl. Equation is still not balanced as the number of H on both sides are not equal. Initially, the number of hydrogen atoms on the reactant side is 6. While on the product side, it is 4. So, to balance the equation, we need to add 2 more hydrogen atoms to the product side. So we shall multiply the HCl compound by 3, giving a reaction ALCl3 plus 3H2O gives ALOH thrice plus 3HCl. Check if the equation is balanced or not. Now, all elements are equal on both sides. It means that this equation is now a balanced chemical equation. Step 4. Write down the final balanced equation again.