An example of a long-standing error in
reaction mechanisms, which we and others have used so often because
it apparently is so well-behaved. The reaction is
and the observed rate equation is
For nearly seventy-five years, everyone
assumed that the process occurred by the collision of one hydrogen
molecule and one iodine molecule, with enough energy to bring about
reaction.
Only as recently as 1967 was it demonstrated
that the actual reaction involves the reversible dissociation of I2
molecules into atoms, followed by the reaction of these I atoms with
H2 :