The reaction of hydrogen and iodine monochloride is given as:
H2(g)+2ICl(g)→2HCl(g)+I2(g)
This reaction is of first order with respect to H2(g) and ICl(g), following mechanisms were proposed :
Mechanism A : H2(g)+2ICl(g)→2HCl(g)+I2(g)
Mechanism B : H2(g)+ICl(g)→HCl(g)+HI(g), slow
HI(g)+ICl(g)→HCl(g)+I2(g), fast
Which of the above mechanism(s) can be consistent with the given information about the reaction?
B only
In multi-step reactions, the slowest step is regarded as the rds or the rate determining step. Hence, the rate expression only takes the slowest step into account.
H2(g)+ICl(g)⟶HCl(g)+HI(g) is first order with respect to H2 and ICl. Therefore, for the given reaction, mechanism (B) is consistent with the given data.