(b) i Table 1 (below) shows the concentration and rate of decomposition for subs
ID: 873601 • Letter: #
Question
(b) i Table 1 (below) shows the concentration and rate of decomposition for substance A measured after 4 consecutive time periods. Calculate the value of m if the decomposition rate is expressed by Equation l (Decomposition rate)- klAl (1) where k rate constant, LA1 is the concentration of reactant A and m is a constant. Table 1 Concentration and reaction rate for decomposition of A 1st period 2nd period 3rd period 4th period X Concentration of A (mol/m3) 2.10 0.90 0.30 Decomposition rate (mol/m's) 1.96 0.36 0.16 IY [1 mark ii. Calculate the rate constant for the reaction in question (b)i. [1 mark iii. Based on the calculation results in questions (bi and (bii, estimate the order of the decomposition reaction. [1 mark iv. Obtain the value X in Table 1 by estimating the concentration of the substance A when the decomposition rate is 0.16 mol/m3s. [1 mark v. obtain the value Y in Table 1 by estimating the rate of reaction when the concentration of A is 0.30 mol/m3 [1 markExplanation / Answer
rate = k[A]^2
b(i) Let us compare the Ist period and the 2nd period,
1st period / 2nd period = [A1]^m/[A2]^m
Feeding the values from the table above,
1.96/0.36 = [2.1/0.9]^m
5.44 = 2.1875^m
Thus m = 2.164
b(ii) Rate constant k
Consider the 1st period,
k = rate / [A]^m
= 1.96 / (2.10)^2.164
= 0.393 s-1
Rate constant = 0.393 s-1
b(iii) The order of the reaction is second order to [A].
b(iv) Lets take m = 2 (approx value from b(i) calculated)
then comparing Ist and 3rd period we get,
rate 1 / rate 3 = [A1]^2 / [A3]^2
feeding the values from the above table,
1.96/0.16 = (2.1)^2/(X)^2
solving for X,
X = 0.6 mol/m^3
b(v) Now compare 4th period with 1st period,
rate 1 / rate 4 = [A1]^2 / [A4]^2
feeding the values from the above table,
1.96/Y = (2.1)^2/(0.3)^2
solving for Y,
Y = 0.04 mol/m^3.s
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