It might help if you look at the imaginary cover of your book and ask yourself what words will get people to open the book. Until you get the book opened you are losing buyers. After it is opened the chapter titles need to keep on selling people on what they will find inside. Your answer needs to be in your query, and in your table of contents. There are many answers to that question.
Some experts insist a query be only one page long, single spaced, and typewritten.
Other experts say you can sometimes go as high as three pages. Most of the queries we send out are three pages long. They are illustrated where possible and if space permits. Many of them are designed to show the editor what a cover of your book might look like, and how the decs and anecdotes would invite readers inside. Your complete manuscript is usually sent out only when editors ask for yours specifically.