hello. My name is***** can help you with your question. Who are you publishing your book with? Are you doing it through Kindle self-publishing? There is really nothing stopping you from putting a single chapter on the Kindle and using it promotionally. Just have it as a separate book with a link back to the full book. If you talk to Amazon or if you're working with create space etc., they can tell you how to do it with their publishing system. My understanding is, however, that they will charge you a small amount for anything you give away for free. But I really don't know how that applies to a single chapter of the book.