Question

if there are 2 grams of product produced by a chemical reaction, how many grams of reactant were consumed

Answer 1

According to the principle of conservation of mass, mass is neither lost nor gained in the course of a chemical reaction. In other words, the total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning. There is, however, a slight caveat. Most chemical reactions are accompanied by a change in energy and typically heat is given out or taken in. This is accompanied by a change in mass which is related to the change in energy according to Einstein’s equation: ΔE = (Δm)c^2. In practice, for most chemical processes, this change in mass is absolutely tiny and beyond current limits of detection. However, nuclear reactions are accompanied by very much larger changes in energy and do result in detectable changes in mass.