Question

What happens to the mass of substances during a chemical change?

Answer 1

"The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction."

source: https://www.nature.com/scitable/knowledge/library/the-conservation-of-mass-17395478/