Given a scientific passage and an answer, generate a question for the given answer.

Passage: Did you ever wonder what happens to a candle when it burns? A candle burning is a chemical change in matter. In a chemical change, one type of matter changes into a different type of matter, with different chemical properties. Chemical changes occur because of chemical reactions. You can see more examples of chemical changes at this URL: http://www. youtube. com/watch?v=66kuhJkQCVM . Answer: chemical reactions
Chemical changes occur because of what?