In a chemical reaction, the structure of atoms as chemical elements is unchanged. Atoms in one element do not become atoms in another element. There is also no loss or creation of new atoms (Lavoisier's Law).
The number of atoms of the reagents must be equal to the number of atoms of the products. When this happens, we say that the chemical equation is balanced.
Balanced Equation Example: C + O2 → CO2
Example of unbalanced chemical equation: H2 + O2 → H2O
Note that in the 1st equation there is a carbon in the reagent and a carbon in the product. There are also two oxygen in the reagent and two in the product. The equation is correctly balanced.
In the 2nd equation, there are two hydrogens in the reagent and two hydrogens in the product, but there are two oxygen in the reagent and only one in the product. So one must balance this equation. There are a few methods for balancing a chemical equation. The easiest and simplest is the retry method.
To balance the 2nd equation, we can put the number 2 in front of the H2 and number 2 in front of H2O, like this:
2 h2 + O2 → 2 H2O
The number of atoms, for example, must always be kept. For this number we give the name of index. The number that can be placed in front of the atom is the coefficientin this case also 2.
So now we have 4 H in the reagent and 4 H in the product. Also 2 O in the reagent and 2 O in the product. The reaction is now balanced. When the coefficient is 1, it does not need to be written.
Trial method / coefficient adjustment
To adjust the chemical reaction coefficients, we use the trial method, which consists only of counting the number of atoms of the reagents and products.
To make things easier, we can start by hitting the metals. Next the nonmetals, then oxygen and lastly hydrogen. In this order: