What Is Conserved in Chemical Reactions?

••• Chemical explosion image by Edwar Xie from Fotolia.com

The Law of Conservation of Matter states that in an ordinary chemical reaction there is no detectable increase or decrease in the quantity of matter. This means that the mass of substances present at the start of a reaction (reactants) must be equal to the mass of those formed (products), so mass is what is conserved in a chemical reaction.

Molecular Weight

The conservation of matter can be illustrated by the reaction of hydrogen (H2) and oxygen (O2) to form water (H2O). A water molecule contains two atoms of hydrogen and one atom of oxygen, so one mole -- the molecular weight in grams -- of water molecules contains two moles of hydrogen and one mole of oxygen. In other words, 2.02 grams of hydrogen react with 16 grams of oxygen to form 18.02 grams of water.

Empirical Formula

The Law of Conservation of Matter can be used to determine the empirical formula – the ratio of the atoms of elements – of an unknown compound.

Atom Economy

The so-called “atom economy” of a reaction indicates the proportion of reactants that are converted into useful products. High atom economy reactions produce less waste and can form part of a strategy for preserving the environment.


About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.

Photo Credits

  • Chemical explosion image by Edwar Xie from Fotolia.com