What are the main themes in chapter 5 of the novel Frankenstein?
I assume you mean Volume 1, Chapter 5 of Frankenstein, and not Volume 2?
The main themes are in bold:
Creation of Life from Death: Victor wants to "infuse a spark of being into the lifeless thing that lay at my feet" and
God vs. Man vs. Monster: Ironically, Victor (a god who can create new life) calls the Monster both a "catastrophe" and a "Beautiful!--Great God!" The duality of horror and fascination of life is prevalent in the Romantic artist.
Fantasy vs. Reality: At once, Victor denies the reality of his creation. He tries to abort it. As such, he exiles both it and himself. As a result, he is haunted by "the wildest dreams." This foreshadows the revenge of the monster against him for abandoning him.
Mythical Allusions: This chapter is like the Biblical Creation of Man in Genesis and the Promethean Myth of Fire and Coleridge's "Rime of the Ancient Mariner." Victor even quotes it: "Like one who, on a lonely road, Doth walk in fear and dread, And, having once turned round, walks on, And turns no more his head; Because he knows a frightful fiend Doth close behind him tread." As such, there is immediate guilt, punishment, and shame involved in the fall of man.