It is apples and oranges. HTML 5 is a language that you use to create web pages. it is as you can guess from the name the 5th and latest version of HTML with a lot of additional features.
Web 2.0 is not a language, it is the concept of sharing and collaboration.
It encourages users not only consume the information, but actively participate in creating content. Blogs, twitters, wiki, one website exposing API and allowing other websites to call it, is all product of Web 2.0 concept.
