Chemical reaction
= Chemical reaction
{wiki}
A <chemical reaction> interconverts <chemical species>, as defined by the https://goldbook.iupac.org/terms/view/C01033[IUPAC Gold Book, chemical reaction]{ref}. The consumed species are <reactants>; the formed species are <reaction products>. In ordinary <chemical reactions>, <chemical atoms> are rearranged while each <chemical element>'s total atom count is conserved. For a complete <chemical equation>, net <electric charge> is conserved too.
For example, the balanced <chemical equation>
$$
2\mathrm{H}_2+\mathrm{O}_2\longrightarrow2\mathrm{H}_2\mathrm{O}
$$
describes conversion of <molecular hydrogen> and <molecular oxygen> into <water>. Both sides contain four <hydrogen> <chemical atoms> and two <oxygen> <chemical atoms>. Three <reactant> <molecules> become two <reaction product> <molecules>: atom counts are conserved, but molecule counts need not be. See https://openstax.org/books/chemistry-2e/pages/4-1-writing-and-balancing-chemical-equations[Flowers et al., Chemistry 2e, balancing chemical equations].
The coefficients describe net consumption and formation, without asserting that three <molecules> collide in one step. A balanced <chemical equation> supplies quantitative constraints; it does not determine how quickly the <chemical reaction> occurs, or whether <chemical equilibrium> prevents complete conversion. Those questions need further information. Keeping these roles distinct makes <stoichiometry> useful even when the microscopic details are complicated.