What is chemical equation a. substance present after a reaction b. reaction in which substances combine to form a more complex compoud c. principle that states that matter if not created of destroyed during a chemical rection d. reaction in which one element replaces another in a compoud e. substance present before a reaction f. number telling how many molecules of a substance are involved in a chemical reaction g. reaction in which compounds are broken down into simpler substances h. uses symbols and formulas to show chemical reactions.