True or false: the mass of the reactants always equal the mass of the products?

Answer 1

This is true in most cases. The main exception is a nuclear reaction. In a nuclear reaction energy is created from "mass" (E=MC^2).

Otherwise, most reaction do follow mass conservation.

Answer 2

yes and no.

For the purpose of your high school chemistry class yes. For a quantum physicist, no. Since most reactions give off energy, that energy is lost. Matter is converted to energy at enormously tiny levels. Even in nuclear reactions, very little mass is converted to energy.

So in short, if you have 100 grams of chemical reactants, you will have 100 grams of products, unless you have a scale that measures to the trillionths of one gram.

Answer 3

Always

Law of Conservation of Mass