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Conservation of Mass in Chemical Reactions

Matter cannot be created or destroyed in chemical reactions.

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Conserving Mass and Energy

Where do mass and energy go in a chemical reaction?

License: CC BY-NC 3.0


We light a fire.  By the end, we notice that there is very little wood left.  What has happened to it?  Has it disappeared or been destroyed?  While the logs are certainly destroyed, the Law of Conservation of Mass stipulates that mass (in this case, the wood) cannot be destroyed or created.

Creative Applications

  1. What has actually happened to the matter in the wood?  It’s clearly not near the log, except for the little bit of ash leftover.  (Hint:  Research the combustion of wood.  What seem to be the products?   Where do these products go?)
  2. In addition to the mass apparently disappearing, energy appears to be forming.  The wood at the start doesn’t seem to have much energy present, as it seems pretty ordinary.  Yet the formation of energy violates the Law of Conservation of Energy, which says that energy cannot be created or destroyed.  So where has this energy come from?  What form was it in, and what form does it become?
  3. Another example of the conservation of energy and mass is the boiling of water.  Where does the energy from heating the water go?  Where does the mass of the water go?  (As you may notice, some water disappears after it's been boiled for an extended period of time.)

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