Here's why:

* Coefficients are the numbers that appear before a chemical formula in a balanced equation. They tell you the number of molecules of each reactant and product involved in the reaction.

* Subscripts are the numbers that appear after an element's symbol in a chemical formula. They indicate the number of atoms of that element within a molecule.

Changing coefficients:

* Adjusts the number of molecules involved in the reaction.

* Allows you to conserve the number of atoms of each element on both sides of the equation.

Changing subscripts:

* Alters the chemical composition of a molecule.

* Creates a different compound entirely.

* This is not allowed when balancing equations!

Example:

Let's take the reaction of hydrogen and oxygen to form water:

* Unbalanced: H₂ + O₂ → H₂O

* Balanced: 2H₂ + O₂ → 2H₂O

To balance the equation, we change the coefficient in front of H₂ to 2 and the coefficient in front of H₂O to 2. This ensures that there are the same number of hydrogen and oxygen atoms on both sides of the equation.