Here's why:
* Coefficients represent the number of moles of each reactant and product. Changing the coefficient changes the number of molecules or moles involved in the reaction.
* Subscripts in a chemical formula represent the number of atoms of each element within a molecule. You cannot change the subscripts because that would change the identity of the substance itself.
For example:
Consider the unbalanced equation:
```
H₂ + O₂ → H₂O
```
To balance this, we adjust the coefficients:
```
2H₂ + O₂ → 2H₂O
```
Explanation:
* Initial state: 2 hydrogen atoms on the left, 2 oxygen atoms on the left, and 2 hydrogen atoms and 1 oxygen atom on the right.
* Balanced state: 4 hydrogen atoms and 2 oxygen atoms on both sides.
By adjusting the coefficients, we ensure that the number of atoms of each element is the same on both sides of the equation, satisfying the law of conservation of mass.
