CBSE Guess > Papers > Important Questions > Class XII > 2013 > Chemistry > Chemical kinetics (Numerical) By Mr. R. Srinivas Vasudevamurthy

CBSE CLASS XII

Chemical kinetics (Numerical)

1. The decomposition ammonia on a platinum surface follows zero order kinetics.
2NH₃(g) N₂(g)+3H₂(g) K= 2.5x10^-4 mole/l/sec. Determine the rate of

a) disapperance of NH₃
b) rate of formation of N₂
c) rate of formation of H₂.

2. The decomposition ammonia on a platinum surface follows zero order kinetics.
Calculate the value of rate constant K and the half life of the reaction. Given

Time (seconds)                     Pressure of NH₃(g) in Pascal
       0                                                        4x10^-2
       100                                                   3.5 x10^-2
       200                                                   3.0 x 10^-2
       300                                                   2.5 x 10^-2

3. A first order reaction is 20% complete in 10 minutes. Determine the time taken for 80% completion of the reaction.

4. 2A +B A₂B  K= 2.5 x10^-4 M^-2 sec^-1 Find the rate when the initial concentrations of [A] = 0.1M   [B] = 0.2 M. Also find the rate when 0.04 moles/litre of A has reacted.Rate=K[A][B]²

5.  For a certain chemical reaction variation in the concentration in [R ] versus time(s) plot is given below

i) what is the order of the reactions?
ii) what are the units of rate constant k?
iii) give the relationship between k and t1/2 
iv) what does the slope of the above line indicate?
v) draw the plot [R ] 0 / [R]  versus time(s)

6. Consider the reaction R  → P. The change in the concentration of R with shown in the following plot.

  i) Predict the order of the reaction.
 ii) Write the expression for half life of this reaction. 

7.  2NO₂+F₂  _2NO₂F Write the rate of reaction in terms of

(a) rate of formation of NO₂F
(b) rate of  disappearance of NO₂
(c) rate of disappearance of F₂

8. The decomposition of NH3 follows zero order. 2 NH₃   N₂+3H₂ Find the rate of production of N₂ and H₂.K=2.5x10^-4MS^-1 −1

9.  2A+B+C_  A₂B+C Rate=K(A)(B)₂ K=2x10_-6M_-2S_-1Calculate the initial rate when

(A)=0.1M 
(B)=0.2M
(C)=0.6M Find the rate when 0.04mole of (A) is consumed.

10. 2NO₂+F₂ _2NO₂F
Experiment          (NO₂)M      (F₂) M            Rate(M/S)
  1                             0.2              0.05                 0.006
  2                             0.4              0.05                 0.012
  3.                            0.8              0.10                 0.048

Find the order with respect to NO₂ and F₂.Also find the overall order of the reaction. Deduce the mechanism of the reaction.

11. Show that(a) 2t½=t¾ (b)Half life of a reaction is 10seconds.Find t_2/3

12. Hydrolysis of methyl acetate in aqueous solution has been studied by titrating liberated acetic acid with NaOH

rate=K(CH₃COOCH₃) (H₂O)
t/min 0                       30                                     60                                                      90
c/M 0.8500                0.8004                              0.7538                                             0.7096

Show that it follows pseudo first order reaction as the concentration of water remains constant (1L of water=1000g) What is the value of K?

13. The rates of a reaction starting with initial concentrations 2x10^-3−3M and1x10^-3M are 2.4x10^-4M/s
    and0.6x10^-4M/s respectively. Find the order of the reaction and rate constant K.

A+5B+6C 3L+3M
Experiment	(A)M	(B)M	(C)M	Rate M/minute
1.	0.02	0.02	0.02	00208
2.	0.01	0.02	0.02	0.00104
3.	0.02	0.04	0.02	0.00416
4.	0.02	0.02	0.04	0.00832

Determine the order with respect to each reactant. Find K .Calculate the initial rate when concentration of each reactant is 0.01M.Find the initial rate of change in concentrations of B and L

14. Rate of a reaction becomes 1.414 times when concentration of the reactant is doubled. Find the order of the reaction.

15. (a) show that for a first order reaction t½ is independent of the initial concentration of the reactant.

(b) show that for a zero order reaction t½ is directly proportional to initial concentration of the reactant and inversely proportional to rate constant.

16. Rate constant of a reaction is 2M ^-1 S ^-1 at 700K and 32 M ^-1 S ^-1 at 800K.Find Ea

17. Rate of a reaction becomes 4 times when temperature changes from 27 ⁰C to 37 ⁰C. Find Ea.

18. Rate constant of a reaction at 700K and 760K are 0.01 M ^-1 S ^-1and 0.105 M ^-1  S ^-1 respectively. Find A and Ea .

19.  Show that for a first order reaction, time required for 99.9% reaction is 10 times the time needed for 50% completion of the reaction.

20. A piece of wood shows C₁₄ activity which is 60% activity found today. Find the age of the sample.t½=5770years.

21. The following data were obtained during the first order decomposition of SO₂Cl₂ at constant
     volume . SO₂Cl₂(g)  SO₂(g) +Cl₂(g)

    Experiment           Time(sec)                  Total pressure(atm)
         1                           0                                     0.5
         2                           100                                0.6
       Calculate the rate when total pressure is 0.65 atmospheres.

22.  2N₂O₅(g) 2 N₂O₄(g) +O₂(g) follows first order kinetics at constant volume.
       Experiment              Time(sec)                    Total pressure(atm)
           1                            0                                       0.5
           2                            100                                  0.512
      Find the value of rate constant K.

23.  The time required for 10% completion of a first order reaction at 298K is equal to that required for
       25%  completion at 308K. Find Ea. Calculate K at 318K.

24. 2HI(g)  H₂(g) +I2(g) Ea at 581K is 209.5KJ/mole. Determine the fraction of molecules
      having energy equal to or greater than Ea.

25. Ea of a reaction is 75 KJ/mole in the absence of a catalyst and 50KJ/mole in the presence of a Catalyst at 300K. Determine the extent to which the rate of reaction is increased.

26. The rate constant for the first order decomposition of H₂O₂ is given as logK = 14.34 – 1.25x 104 K/T. Calculate Ea for this reaction. At what temperature will its half life be 256 minutes?

27. The decomposition of hydrocarbon follows the equation K = (4.5x 1011 sec-1) e-28000K/T
      Calculate Ea

28. 2NO(g) + O₂(g) 2NO₂(g) occurs in one step. What will happen to the rate when the Volume of the reaction vessel is reduced to 1/3 of the original volume?

29. A reaction is first order with respect to A and second order with respect to B. What will happen to                the rate if concentration of A and B are doubled?

30. Rate of a reaction becomes 1.414 times when concentration of the reactant is doubled. Determine the order of the reaction.

31. Rate constant K of a reaction varies with the temperature according to the equation logK = constant- Ea/2.303RT where Ea is activation energy of the reaction. When a plot of logK vs 1/T , a straight line with a slope – 6670K is obtained. Find Ea. [R=8.314J/K/mole]

32.  The possible mechanism for the reaction

2 NO(g)+O₂(g)  2 NO₂(g) is

      i)  NO(g) +O₂(g)   NO₃(g) [Fast]

      ii)  NO₃(g) +NO(g)    NO₂(g)+NO₂(g) [slow]

 

Submitted By : Mr. R. Srinivas Vasudevamurthy
Email: [email protected]