Explosions occur when the rate of one or more steps in a reaction suddenly increases in a very short period of time. The sudden increase in the rate could be due to autocatalysis (i.e., a radical once produced, goes on producing more radicals of the same type). Often, the heat produced in reactions is so large that the container can not accommodate the heat, leading to an explosion. We will illustrate a mechanism for explosion through the H2 + O2 reaction, which involves the participation of radicals such as H, O, OH, HO2
The major steps in this explosion reaction are :
H2 + O2 H+ HO2 (initiation)
HO2 + H2 H2O + HO (propagation)
HO + H2 H2O + H (propagation)
H+ O2 HO + O (branching)
O + H2 HO + H (branching)
(30.20)
The dots on H, OH etc represent radicals (containing unpaired electrons). For explosions to occur, the reaction mixture needs to attain specific temperatures and pressures. These ranges are shown in the figure below.
Figure 30.1 Pressure vs temperature for an explosion reaction showing several explosion limits.
, O
H
