If I have 6HCl, why can't I change the subscripts and write 3H2Cl2?

1 Answer
Truong-Son N.
May 7, 2017

Because H2Cl2 and HCl are completely different molecular connections. Consider the following:

  • The first column is what we mean by having six HCl molecules.

  • The second column is when we draw out what it literally means to have three H2Cl2 molecules (and the red means it's a very problematic structure according to MarvinSketch).

  • The third column is what we mean by three H2 and three Cl2 molecules.

Those are three ways to depict the combination of six H and six Cl atoms... and they are all quite different.

So just know that when we write out chemical formulas, we specify very particular molecular structures. We can't balance reactions using subscripts (unless the reaction had a typo or something).

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