So defosphorylation of ATP is a very exergonic reaction and it releases a large amount of free energy and that's precisely why this reaction itself is thermodynamically stable. In fact, because the products are so much more stable than the reactants. This reaction ultimately takes place in a single direction. So it takes place this way and this reverse reaction doesn't actually take place, at least not at a very high rate. And that leads us directly into number seven. So if the process of asphorylation is to actually be a convenient process, we have to actually be able to reverse this process.