What is a chemical reaction?

A chemical reaction is material changing from a beginning mass
to a resulting substance. The hallmark of a chemical reaction
is that new material or materials are made, along with the
disappearance of the mass that changed to make the new. This
does not mean that new elements have been made. In order
to make new elements, the nuclear contents must change.
There are magnitudes of difference in the amounts of energy in
ordinary chemical reactions compared to nuclear reactions.
The energy of rearrangement of the nuclei of atoms to change to new
elements is enormous compared to the smaller energies of
chemical changes. The alchemists, in their efforts to change less
expensive metals to gold, did not have the fundamental
understanding of what they were attempting to do to appreciate
the difference.

A chemical equation is a way to describe what goes on in a
chemical reaction, the actual change in a material. Chemical
equations are written with the symbols of materials to include
elements, ionic or covalent compounds, aqueous solutions,
ions, or particles. There is an arrow pointing to the right that
indicates the action of the reaction. The materials to the left
of the arrow are the reactants, or materials that are
going to react. The materials to the right of the arrow are the
products, or
materials that have been produced by the reaction. The Law of
Conservation of Mass
states that in a chemical reaction no
mass is lost or gained. The Law of Conservation of Mass applies
to individual types of atom. One could say that for any
element, there is no loss or gain of that element in a chemical
reaction. There are such things as reversible reactions,
reactions in which the products reassemble to become the original
products. Reversible reactions are symbolized in chemical
equations by a double-headed arrow, but the standard remains to
call the materials on the left the reactants and the materials
on the right the products.

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