Okay kiddo, let me explain what an isodesmic reaction is.
Let's pretend we have a bunch of Lego blocks. We can stick them together in different ways to make different shapes, right? That's kind of like how molecules work. Molecules are made of atoms that can combine in different ways to make different molecules.
Now, sometimes when we combine atoms to make a molecule, it takes more energy to do it than the energy we get out of the final product. That's like using more Lego blocks than we end up with in our final shape.
But sometimes, the energy we put into making the molecule is equal to the energy we get out of it. That's like using the same number of Lego blocks for our shape as we end up with. We call this an isodesmic reaction - iso means "same," and desmic means "bonding."
So basically, an isodesmic reaction is when we combine atoms to make a molecule and the energy we put in is the same as the energy we get out. It's like using the same number of Lego blocks for our final shape as we started with. Pretty cool, huh?