Chemistry That Goes Both Ways

Most reactions seem one-way — once you burn paper, you can't unburn it. But many reactions can actually run in reverse! Heat blue copper sulfate crystals and you get white anhydrous copper sulfate plus steam. But add water to the white powder, and it turns blue again, releasing heat. The same atoms, switching between two forms. These reversible reactions are everywhere — from the Haber process making fertiliser to your blood carrying oxygen. Understanding them is key to controlling industrial chemistry.