The Chemical reaction, 2HCl + N2O5--> 2NO2 + Cl2 + H2O, is performed under two s

Question

The Chemical reaction, 2HCl + N2O5--> 2NO2 + Cl2 + H2O, is performed under two sets of conditions. In the first experiment, the initial concentrations of N2O5 and HCl were 0.080M and 2.0M, respectively. In the second experiment the initial concentrations of N2O5 and HCl were 0.050M and 3.0M, respectively. Both experiments were conducted at 27 celcius.

a) Compare the average rate of reaction in the second experiment over the first 60s of the reaction to the average rate of reaction in the first experiment over the same concentration range. What conclusion may be drawn about the order of the reaction with respect to [HCl]? Show all relevant work.

b) Compare the tim es it takes for the first reaction to go from 0.080M to 0.040M to the time it takes for the first reaction to go from 0.040M to 0.020M. What does this indicate about the order of the reaction in [N2O5]? Justify answer.

c) What is the rate law for for this reaction?

d)What is the rate constant for this reaction?

e)How long will it take for 90% of the N2O5 to be consumed under the conditions of the first experiment?

f) Write a possible mechanism for this reaction. Indicate the rds.

Explanation / Answer

a) average rate in Expt. 1 over 0-60 s = -(0.05-0.08/60) = 5 x 10^-4 M/s

average rate in Expt. 2 over 0-60 s = -(0.031-0.05/60) = 3.17 x 10^-4

The average rate of Expt 1. is greater then the avearge rate of Expt. 2 in first 60 s. With respect to HCl the order would be 1.7 or roughly 2.

b) For the first Expt. 1

Time taken to go from 0.08 M to 0.04 M = 75 s

Time taken to go from 0.04 M to 0.02 M = 35 s

So looking at the data we can see that time required is reduced to half from 75-110 to 0-75 s. Thus the order with respect to [N2O5] is 1.

c) The rate law for the reaction would be,

rate = k[N2O5]^1[HCl]^2

d) Rate constant k would be,

k = 0.0005/(0.03)^2(0.03) = 18.52 M-2.s-1

e) To complete 90% os reaction, the Expt. 1 takes 300 s

f) A possible mechanism for the reaction woud be,

N2O5 <==> NO2 + NO3

NO3 + HCl <==> NO2 + HOCl

HOCl + HCl ---> Cl2 + H2O

Overall reaction,

N2O5 + 2HCl ---> Cl2 + 2NO2 + H2O

the RDS of the reaction could be the first step.

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