Consider the following reaction depicting the chlorination of dimethenamid (DM-H
ID: 536434 • Letter: C
Question
Consider the following reaction depicting the chlorination of dimethenamid (DM-H) by chlorine monoxide (Cl2O) to give chlorodimethenamid (DM-Cl) and hypochlorous acid (HOCl):
DM-H + Cl2O à DM-Cl + HOCl
The reaction is depicted as only proceeding in the forward direction (i.e., irreversibly) because the rate of the reverse reaction is negligibly small. The rate constant for the forward reaction (at 25 °C) is 1.37 x 106 M–1 s–1. In a solution initially containing 0.5 µM of DM-H under conditions representative of drinking water chlorination (pH 7.0, [HOCl]o = 21 µM, 25 °C), the formation rate of DM-Cl is 2.7 ´x10–6 µM s–1. Everything else equal, what would the formation rate of DM-Cl be if the initial amount of HOCl were increased by a factor of 2 (i.e., [HOCl]o = 42 µM)?
Explanation / Answer
Here it is clearly mentioned that the reaction is irreversible because rate of the reverse reaction is negligibly small compared to rate of forward reaction.
Now we can express the rate equation for backward reaction in the terms of concentrations of products
but even if we increase the concentration of HOCl since the rate constant of backward reaction is negligible it dont have much effect on the reaction. So eventhough the concentration of HOCl is increased reaction kinetics wil no change much bu still it will result into small decrease in formation of DMCl which is not quanifiable.