2HI ® H2 + I2
Trimolecular or termolecular reactions involve simultaneous collision
between three reacting species, for example,
2NO + O2 ® 2NO2
The probability that more than three molecules can collide and
react simultaneously is very small Hence, reactions with the
molecularity three are very rare and slow to proceed It is, therefore, evident that complex reactions involving more than
three molecules in the stoichiometric equation must take place in more
than one step KClO3 + 6FeSO4 + 3H2SO4 ® KCl + 3Fe2(SO4)3 + 3H2O
This reaction which apparently seems to be of tenth order is actually
a second order reaction