# Why is predicting products of chemical reactions difficult? [closed]

I was going to ask whether there are software that could be used to predict the products of any given chemical reaction. However, I then noticed these two earlier questions

where it is said such predictions are too difficult to make. What makes the prediction difficult?

• Welcome to chemistry.SE! If you had any questions about the policies of our community, you can ‎visit the help center or take a ‎‎tour of the website. – M.A.R. Jan 26 '15 at 15:33
• I can give you a short answer: Mainly because there isn't only one type of chemical reaction and there aren't only a few factors that have to be taken into account when predicting. But I think "good answers are going to be too long for this format". – M.A.R. Jan 26 '15 at 15:50
• I don't get why this was put on hold. The answer does not necessarily need to be overly long. DavePhD already provided some good basic information. – char Jan 26 '15 at 18:25
• Dave provided a simple (no, not really!) example of how predicting the result would be hard. He didn't give all the reasons, but one. And I'm not the only guy with this idea, I suppose. – M.A.R. Jan 26 '15 at 18:58

Even solving the time independent non-relativistic Schrodinger equation for $\ce{H2+}$ in isolation, where there is only one electron and two protons involves approximating the protons as fixed relative to each other.
Now imagine trying solving a system of $10^{23}$ molecules each having multiple nuclei, and dozens or even hundreds of electrons, and including time dependence!