few chemical reactions are spontaneous decompositions of molecules,
with first-order kinetics and equilibium as in the crabapple war.
First-order kinetics are encountered more commonly in radiochemistry
and the decay of atomic nuclei. Most chemical reactions occur when
two or more molecules or ions collide, so the rates of reaction
depend simultaneously on the concentrations of more than one substance.
the hydrogen-iodine reaction,
one molecule of hydrogen gas must interact with one molecule of
iodine vapor for chemical reaction to take place.