For a reaction:
aA→bB
a,b are stoichiometric coefficients of reactant A and product B respectively
Rate=−1a×d[A]dt=+1b×d[B]dt
So, for the reaction:
BrO−3(aq)+5Br−(aq)+6H+→3Br2(l)+3H2O(l)
Writing rate in terms of Br− and Br2
Rate=−15×d[Br−]dt=+13×d[Br2]dt
⇒d[Br2]dt=−35d[Br−]dt.....eqn1
Given:
d[Br2]dt=k[Br−][BrO3][H+]2......eqn(2)
−d[Br−]dt=k′[Br−][BrO3][H+]2.......eqn(3)
Substituting equation (1) in (3), we get,
53d[Br2]dt=k′[Br−][BrO3][H+]2
d[Br2]dt=35k′[Br−][BrO3][H+]2.....eqn(4)
From equation (2) and (4),
1=53kk′
3k′=5k