Question

Describe the hit-and-trial method for balancing chemical equations.

Answer 1

Hit-and trial method: The hit-and-try method is used to adjust the coefficients in the formulae of the reactants and products so that the total number of atoms of each element on both sides of the equation is equal.

Balanced chemical equation:

A chemical equation in which the number of atoms of each element on both sides of the equation is equal is called a balanced chemical equation.

Step-1: Start balancing from the element (other than O and H) that appears least in the equation.

Step-2: Balance oxygen and hydrogen.

Step-3: Check again to be sure that the equation is balanced.

Let's consider an equation : $\mathrm{Fe}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\to {\mathrm{Fe}}_3{\mathrm{O}}_4\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Step-1: Analyze the number of atoms of reactants and the number of atoms of products

Elements	No. of atoms (reactants)	No. of atoms (Products)
Fe	1	3
H	2	2
O	1	4

Step-2: Consider the Fe atom. We can multiply 3 in the reactant (Fe) to get the same number of atoms in the product (Fe₃O₄).

Step-3: Hydrogen atoms are balanced.

Step-4: By multiplying 4 in the reactant (H₂O), we can obtain the same number of oxygen atoms on both sides.

$3\mathrm{Fe}\left(\mathrm{s}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\to {\mathrm{Fe}}_3{\mathrm{O}}_4\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Elements	No. of atoms(reactants)	No. of atoms (products)
Fe	3	3
H	8	2
O	4	4

Step-5: Let us now examine hydrogen atoms. Multiplying 4 in the product (in H₂), we obtain the same number of hydrogen atoms as in the reactants.

Elements	No. of atoms (reactants)	No. of atoms (products)
Fe	3	3
H	8	8
O	4	4

Hence, we can write: $3\mathrm{Fe}\left(\mathrm{s}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\to {\mathrm{Fe}}_3{\mathrm{O}}_4\left(\mathrm{s}\right)+4{\mathrm{H}}_2\left(\mathrm{g}\right)$

Now, we can say that equation is balanced.