12TH CHEMISTRY UNIT WISE
IMPORTANT QUESTIONS
LESSON- 7 chemical kinetics
TEXT BOOK QUESTION
TWO MARK:
1. Define average rate and instantaneous rate.
2. Define rate law and rate constant
3. Write the rate law for the following reactions.
a.A reaction that is 3/2 order in x and zero order in y.
b.A reaction that is second order in NO and first order in Br2. 4.
4. For a reaction X + Y + Z ⎯⎯→ products the rate law is given by rate = k [X 3/2 [Y] 1/2. What is the overall order of the reaction and what is the order of the reaction with respect to z.
5. Write Arrhenius equation and explains the terms involved.
6. The decomposition of Cl2O7 at 500 K in the gas phase to Cl2 and O2 is a first order reaction. After 1 minute at 500K, the pressure of Cl2O7 falls from 0.08 to 0.04 atm.
7. Explain pseudo first order reaction with an example.
8. Identify the order for the following reactions (i)Rusting of Iron (ii) Radioactive disintegration of 92U 238 (iii) 2A + 3B ⎯⎯→ products ; rate = [A]1/2 [B]2
9. How do concentrations of the reactant influence the rate of reaction?
10. How do nature of the reactant influence rate of reaction. (or) C where as Titration between potassium per magnate and oxalic acid is carried out at 60 titration between potassium per manganate and ferrous ammonium sulphate at room temperature. Give reason.
11. The rate constant for a first order reaction is 1.54 × 10 – 3 s – 1 . Calculate its half life time.
12. Consider the oxidation of nitric oxide to form NO2 2NO(g) + O2(g) ⎯⎯→ 2NO2 (g)
a.Express the rate of the reaction in terms of changesin the concentration of NO, O2 and NO2.
b.At a particular instant, when [O2] is decreasing at 0.2 mol L–1 s –1 at what rate is [NO2] increasing at that instant?
13. What is the order with respect to each of the reactant and overall order of the following reaction?
a.(a) 3 5Br −(aq) + BrO− (aq) + 6H+ (aq) ⎯⎯→ 3Br2(l) +3H2O(l) The experimental rate law is Rate = k [Br– ] [BrO3] [H+ ] 2
b.CH3 CHO(g) ⎯⎯→ CH 4 (g) + CO(g) 3 the experimental rate law is 3/2 Rate k[CH3CHO]3/2
THREE MARK
1. Derive integrated rate law for a zero order reaction A ⎯⎯→ product.
2. Define half life of a reaction. Show that for a first order reaction half life is independent of initial concentration.
3. What is an elementary reaction? Give the differences between order and molecularity of a reaction.
4. Explain the rate determining step with an example
5. Describe the graphical representation of first order reaction.
6. Explain the effect of catalyst on reaction rate with an example.
7. The rate law for a reaction of A, B and L has been found to be rate = k [A]2 [B] [L]3/2. How would the rate of reaction change when
(i)Concentration of [L] is quadrupled
(ii)Concentration of both [A] and [B] are doubled
(iii) Concentration of [A] is halved
(iv) Concentration of [A] is reduced to (1/3) and concentration of [L] is quadrupled.
8. The rate of formation of a dimer in a second order reaction is 7.5 × 10 – 3 mol L – 1 s – 1 at 0.05mol L – 1 monomer concentration. Calculate the rate constant.| Explain briefly the collision theory of bimolecular reactions. (or) Derive k=pze-Ea/ RT
9. For the reaction 2x + y ⎯⎯→ L. Find the rate law from the following data.
[x] (min) [y] (min) rate (M s – 1 )
0.2 0.02 0.15
0.4 0.02 0.30
10. A zero order reaction is 20% complete in 20 minutes. Calculate the value of the rate constant. In what time will the reaction be 80% complete?
11. From the following data, show that the decomposition of hydrogen peroxide is a reaction of the first order :
1(min) 0 10 20
V(ml). 46.1 29.8 19.4
Where t is the time in minutes and V is the volume of standard KMnO4 solution required for titrating the same volume of the reaction mixture
12. A first order reaction is 40% complete in 50 minutes. Calculate the value of the rate constant In what time will the reaction be 80%c complete
13. Rate constant k of a reaction varies with temperatureT according to the followingA Arrheniusequation log k = log A- Ea/ 2.303R(1/T) WhereEa is the activation energy. When a graph is plotted for log k Vs 1/ T a straight line with a slopeof –4000 K is obtained. Calculate the activationenergy.
14. A first order reaction takes 8 hours for 90% completion Calculate the time required for 80% completion (log 5 = 0.6989 ; log 10 = 1)
15. The rate of the reaction x + 2y → product is–3mol L –1 s –1 if [x] = [y] = 0.2 M and 10 –2 s–1 –2 s –1, What is the overall order of the reaction.
FIVE MARK:
1. A gas phase reaction has energy of activation 200 kJ mol – 1 . If the frequency factor of the reaction is 1.6 × 1013 s – 1 . Calculate the rate constant at 600 K. (e − 40.09 = 3.8 × 10 – 18)
2. The half life of the homogeneous gaseous reactionSO2Cl2 ⎯⎯→ SO2 + Cl2 which obeys first orderkinetics is 8.0 minutes. How long will it takefor the concentration of SO2Cl2 to be reducedto 1% of the initial value?
3. The time for half change in a first order decompositionof a substance A is 60 seconds. Calculatethe rate constant. How much of A will beleft after 180 seconds.
4. The activation energy of a reaction is 225 k cal mol– 1 and the value of rate constant at 40 0c ie 1.8 × 10 – 5 s – 1 . Calculate the frequency factor A.
5.The rate constant of a reaction of a reaction at 400 and 200 K are 0.04 and 0.02 s –1 respectively Calculate the value of activation energy
6. Show that in case of first order reaction, the time required for 99.9%completion is nearly ten Times the time required for half completion of the reaction.
7. The half life of a first order reaction x →products is 6.932 x 104s at 500 K. What percentage of would be decomposed on heating at 500 K for 100 min. (e0.06 = 1.06)
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