Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

Class 12 Chemistry 35 Years JEE Mains &Advance Past yr Paper

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11. The nucleidic ratio,   Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev in a sample of water is 8.0 × 10–18 : 1. Tritium undergoes decay with a half life period of 12.3 years. How many tritium atoms would 10.0 g of such a sample contain 40 years after the original sample is collected?             (1992 - 4 Marks)

Solution: 

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
No. of atoms left after 40 years are derived as follows using the relation
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

 

12. A first order reaction A→ B , requires activation energy of 70kJ mol–1. When a 20% solution of A was kept at 25°C for 20 minutes, 25% decomposition took place. What will be the percent decomposition in the same time in a 30% solution maintained at 40°C? Assume that activation energy remains constant in this range of temperature. (1993 - 4 Marks)

Solution: 

 Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev


13. The gas phase decomposition of dimethyl ether follows first order kinetics.
   CH3 -O- CH3(g) → CH4(g) + H2(g) + CO(g)
The reaction is carried out in a constant volume container at 500°C and has a half life of 14.5 minutes. Initially, only dimethyl ether is present at a pressure of 0.40 atmosphere.
What is the total pressure of the system after 12 minutes? Assume ideal gas behaviour.             (1993 - 4 Marks)

Solution: 
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
Since volume and temp. are constant, final pressure :
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
Hence total pressure = 0.4 – 0.175 + 3 × 0.175 = 0.749 atm

 

14. The progress of the reaction, A    Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev  nB  with time, is presented in figure given below. Determine 

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

(i) the value of n
(ii) the equilibrium constant, K and
(iii) the initial rate of conversion of A.             (1994 - 3 Marks)

Solution: 

(i) According to Fig. in the given time of 4 hours (1 to 5) concentration of A falls from 0.5 to 0.3 M, while in the same time concentration of B increases from 0.2 M to

0.6 M.

Decrease in concentration of A in 4 hours

= 0.5 – 0.3 = 0.2 M

Increase in concentration of B in 4 hours

= 0.6 – 0.2 = 0.4 M

Thus increase in concentration of B in a given time is twice the decrease in concentration of A. Thus n = 2.
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

 

15. From the following data for the reaction between A and B.                (1994 - 5 Marks)

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

Calculate
   (i) the order of the reaction with respect to A and with
   respect to B,
   (ii) the rate constant at 300K
   (iii) the energy of activation, and
   (iv) the pre-exponential factor

Solution:

Let the order with respect to A is x and the order with respect to B is y

 Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
∴ The rate equation for the reaction is

Rate = k [A]2[B]

(i) Thus order of reaction with respect to A = 2 and order of reaction with respect to B = 1.

(ii) Rate constant (k1) at 300 K
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
(iii) Determination of energy of activation :Rate constant (k2) at 320 K
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
(iv) Determination of the pre-exponential factor
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev


16. One of the hazards of nuclear explosion is the generation of 90Sr and its subsequent incorporation in bones. This nuclide has a half-life of 28.1 years. Suppose one microgram was absorbed by a new-born child, how much 90Sr will remain in his bones after 20 years?                (1995 - 2 Marks)

Solution: 

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev 


17. At 380°C, the half-life period for the first order decomposition of H2O2 is 360 min. The energy of activation of the reaction is 200 kJ mol-1 . Calculate the time required for 75% decomposition at 450°C.                    (1995 - 4 Marks)

Solution:
 Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

On usual calculations, k723 K =6.81 ×10–2 min–1

Calculation of time for 75% decomposition at 723 K

Let the initial amount of H2O2, a = 1

∴ Amount at the required time, (a – x) = 0.25

Substituting the values in the given relation,

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

 

18. 227Ac has a half-life of 21.8 years with respect to radioactive decay. The decay follows two parallel paths. one leading to 227Th and the other to 223Fr. The percentage yields of these two daughter nuclides are 1.2 and 98.8 respectively. What are the decay constants (l) for each of the separate paths?            (1996 - 2 Marks)

Solution: 

 Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev


19. The ionisation constant of  Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev in water is 5.6×10–10 at 25°C. The rate constant for the reaction of Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev and OH- to form NH3 and H2O at 25°C is 3.4×1010 L mol–1s–1. Calculate the rate constant for proton transfer from water to NH3.            (1996 - 3 Marks)

Solution: 

 Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

20. The rate constant for the first order decomposition of a certain reaction is described by the equation

Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev              (1997 - 5 Marks)

(i) What is the energy of activation for this reaction?
(ii) At what temperature will its half-life period be 256 minutes?

Solution: 
(i) The Arrhenius equation is

k = A exp (–Ea/RT)

Taking natural logarithm, we get

ln k = ln A – Ea/RT
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

(ii) The reaction is first order as the unit of rate constant is s–1. For a first order reaction,
Subjective Type Questions: Chemical Kinetics & Nuclear Chemistry- 2 | JEE Advanced Notes | EduRev

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