Chapter 4 : Chemical Kinetics
Q. The decomposition of dimethyl ether leads to the formation of CH4, H2 and CO and the reaction rate is given by:
Rate=k[CH3OCH3]3/2

The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether.

i.e., Rate=k[PCH3OCH3]3/2

If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?
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Q. For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.
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Q. During nuclear explosion, one of the products is 90Sr with half life of 28.1 yr. If 1μg of 90Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 year and 60 year if it is not lost metabolically.
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Q. Mention the factors that affect the rate of a chemical reaction.
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Q. In a pseudo first order hydrolysis of ester in water the following results were obtained:
 t/s 0 30 60 90 [Ester]/M. 0.55 0.31 0.17 0.085
(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(ii) Calculate the pseudo first order rate constant for the hydrolysis of ester.
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Q. A first order reaction takes 40 min for 30% decomposition. Calculate t1/2.
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Q. The experimental data for decomposition of N2O5 [2N2O54NO2+O2] in gas phase at 318K are given below:

 t/s 0 400 800 1200 1600 2000 2400 2800 3200 102×[N2O5]/molL−1 1.63 1.36 1.14 0.93 0.78 0.64 0.53 0.43 0.35

(i) Plot [N2O5] against t.
(ii) Find the half-life period for the reaction.
(iii) Draw a graph between log[N2O5] and t.
(iv) What is the rate law?
(v) Calculate the rate constant.
(vi) Calculate the half-life period from k and compare it with (ii)
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Q. In a reaction between A and B, the initial rate of reaction (r0) was measured for different initial concentrations of A and B as given below:

 A/molL−1 0.20 0.20 0.40 B/molL−1 0.30 0.10 0.05 r0/molL−1s−1 5.07×10−5 5.07×10−5 1.43×10−4

What is the order of the reaction with respect to A and B?
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Q. For the decomposition of azo-isopropane to hexane and nitrogen at 543K, the following data are obtained.
 t(sec) P(mm of Hg) 0 35.0 360 54.0 720 63.0
Calculate the rate constant.
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Q. Calculate the half life of a first order reaction from their rate constants given below:
(a) 200s1; (b) 2 min1; (c) 4year1.
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Q. The rate constant for a first order reaction is 60 s1. How much time will it take to reduce the initial concentration of the reactant to its 1/16th value?
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Q. The reaction between A and B is first order with respect to A and zero order with respect to B. Fill in the blanks in the following table:

 Experiment [A]/molL−1 B]/molL−1 Initial rate/ molL−1min−1 I 0.1 0.1 2.0×10−2 II - 0.2 4.0×10−2 III 0.4 0.4 - IV - 0.2 2.0×10−2
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Q. A reaction is second order with respect to a reaction. How is the rate of reaction affected if the concentration of the reactant is : (a) doubled, (b) reduced to 1/2?
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Q. From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.
(i) 2NO(g)N2O(g); Rate=k[NO]2
(ii) H2O2(aq)+3I(aq)+2H+2H2O(I)+3I; Rate=k[H2O2][I]
(iii) CH3CHO(g)CH4(g)+CO(g); Rate=k[CH3CHO]3/2
(iv) C2H5Cl(g)C2H4(g)+HCl(g); Rate=k[C2H5Cl]
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Q. The rate for the decomposition of NH3 on platinum surface is zero order. What are the rate of production of N2 and H2 if K=2.5×104mol litre1s1.
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Q. A reaction is first order in A and second order in B :
(i) Write differential rate equation.
(ii) How is the rate affected when the concentration of B is tripled?
(iii) How is the rate affected when the concentration of both A and B is doubled?
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Q. The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood had only 80% of the 14C found in a living tree. Estimate the age of the sample.
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Q. The following results have been obtained during the kinetic studies of the reaction:
2A+BC+D

 Experiment [A]/molL−1 [B]/molL−1 Initial rate of formation of D/molL−1min−1 I 0.1 0.1 6.0×10−3 II 0.3 0.2 7.2×10−2 III 0.3 0.4 2.88×10−1 IV 0.4 0.1 2.40×10−2

Determine the rate law and the rate constant for the reaction.
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Q. What is the effect of temperature on the rate constant of a reaction? How can this effect of temperature on rate constant be represented quantitatively?
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Q. For the reaction:
2A+BA2B, the rate =k[A][B]2 with k=2.0×106mol2L2s1.
Calculate the initial rate of the reaction when [A]=0.1molL1, [B]=0.2 molL1. Calculate the rate of reaction after [A] is reduced to 0.06 molL1.
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