Ammonia is a common constituent of many natural waters and wastewaters. when water containing ammonia is treated at a water treatment plant, the ammonia reacts with the disinfectant hypochlorous acid (HOCl) in solution to form monochloroamine (NH2Cl) as follows:

NH3 + HOCl > NH2Cl + H2O

The rate law for this reaction is:

d[NH3]/dt = -k[HOCl][NH3]

a) what is the reaction order with respect to NH3?
b) What order is this reaction overall?
c) If the HOCl concentration is held constant and equals10^-4 M, and the rate constant equals 5.1 x 10^6 L/moles-s, calculate the time required to reduce the concentration of NH3 to one half its original value.

Explanation:

(a): The given rate law for the reaction is

d[NH3]/dt = -k[HOCl]x[NH3]

The power of the concentration of NH3, [NH3] in the above rate law expression is 1. Hence the reaction order with respect to NH3 is 1.

(b): In the rate law expression, power of the concentration of NH3 is 1 and also the power of the concentration of HOCl is 1. Hence the overall order of the reaction is 1+1 = 2

(c): Given rate constant, k = 5.1x 106 L/moles.s

Concentration of HOCl, [HOCl] = C = 10-4 M which is kept constant through out the reaction.

Let Initial concentration of NH3, [NH3]i = a M

Hence the final concentration of NH3, [NH3]f = (a - x) = (a - a/2) = a/2 M

Since the concentration of HOCl, C is kept constant, the integrated rate law for this reaction will be like that of a first order reaction with division by HOCl concentration, C.

t = (1 / kxC) x ln [a / (a - x)]

=> t = [1 / (5.1x 106 L/moles.s x 10-4 M)] x ln( a / a/2)

=> t = [1 / (5.1x 106 L/moles.s x 10-4 M)] x ln(2) = 0.00136 sec (answer)

Note: Please check given the value of rate constant, k, as i have doubt that might be wrong. If it is correct then no problem.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error