Why can you add coefficients to an equation but not change subscripts of a formula?

Answer 1

In a chemical formula, changing the coefficient only changes the amount of the substance present. Changing a subscript changes the number of atoms in the compound, thus changing the chemical properties of the compound.

Answer 2

The molecules don't change. For example, when you make water, which is H2O - water is always H2O To make water you need O2 and H2, which don't normally exist as H or O. Ok, now we know what we need, and that won't change, Right. Now, lets set up the reaction:

O2 + H2 --> H2O Got that?

But that equation isn't balanced, so we need to change the number of molecules of the chemicals (That is what coefficients are for): O2 + 2H2 --> 2H2O

All we do by changing the coefficient is to change the amount we are reacting, not the chemical makeup of the substance.

Answer 3

In an equation, coefficients represent the number of units of each element or compound present, so they can be changed to balance the equation without altering the identity of the substances involved. However, changing subscripts in a chemical formula alters the composition and identity of the substance, so they cannot be modified arbitrarily without changing the nature of the compound.