4 ×× 10–5 mol L–1s–1
Now consider a reaction
Hg(l) + Cl2 (g) ® HgCl2(s)
Where stoichiometric coefficients of the reactants and products are
same, then rate of the reaction is given as
[
]
[
]
[
]
2
2
Hg
Cl
HgCl
Rate of reaction = –
–
t
t
t
∆
∆
∆
=
=
∆
∆
∆
i e , rate of disappearance of any of the reactants is same as   the rate
of appearance of the products But in the following reaction, two moles of
HI decompose to produce one mole each of H2 and I2,
2HI(g)   ®   H2(g)   +   I2(g)
For expressing the rate of such a reaction where stoichiometric
coefficients of reactants or products are not equal to one, rate of
disappearance of any of the reactants or  the rate of appearance of
products is divided by their respective stoichiometric coefficients