Q24 of 26 Page 1

(a) Define the following terms:

(i) Activation energy


(ii) Rate constant


(b) A first order reaction takes 10 minutes for 25% decomposition. Calculate t1/2 for the reaction.


(Given: log2 = 0.3010, log3 = 0.4771, log4 = 0.6021)


OR


(a) For a chemical reaction R → P, the variation in the concentration, ln[R] vs. time(s) plot is given as



(i) Predict the order of the reaction.


(ii) What is the slope of the curve?


(iii) Write the unit of rate constant for this reaction.


(b) Show that the time required for 99% completion is double of the time required for the completion of 90% reaction.


(a) (i) Activation energy is the energy required to form an intermediate (activated complex).


(ii)Rate constant of the reaction is defined as the rate of the reaction when concentration of each reactant is unity.


We know that,


When concentration of A and B is 1 then, Rate = k


(b) Given:


• T=10mins


•


For a first order reaction,



Substituting the given values,



We get k=4.79×10-4 s-1


For half life,


Substituting k in above equation we get,




OR


(a) (i) since R → P , it is a first order reaction.


(ii) Since the concentration is decreasing with type, slope is negative.


(iii) Unit of rate constant for 1st order reaction,



(b) For a first order reaction,



Rearranging we get,



Where is the initial concentration of reactants and is the concentration of reactants left unreacted.


Time required for 99% completion,




………………….(1)


Time required for 90% completion,




……………………….(2)


From equations (1) & (2) we can see that the time required for 99% completion is double of the time required for the completion of 90% reaction.


More from this chapter

All 26 →
22

An element X (molar mass = 60 g mol-1) has a density of 6.23 g cm-3. Identify the type of cubic unit cell, if the edge length of the unit cell is 4× 10-8 cm.

 23

Seeing the growing cases of diabetes and depression among children, Mr. Chopra, the principal of one reputed school organized a seminar in which he invited parents and principals. They all resolved this issue by strictly banning the junk food in schools and by introducing healthy snacks and drinks like soup, lassi, milk, etc. in school canteens. They also decided to make compulsory half an hour physical activity for the students in the morning assembly daily. After six month, Mr. Chopra conducted the health survey in most of the schools and discovered a tremendous improvement in the health of students.

After reading the above passage, answer the following questions;


(i) What are the values (at least two) displayed by Mr. Chopra?


(ii) As a student, how can you spread awareness about this issue?


(iii) Why should antidepressant drugs not be taken without consulting a doctor?


(iv) Give two examples of artificial sweetners.


 25

(a) Account for the following:

(i) Bond angle in N is higher than NH3.


(ii) H2S has lower boiing point than H2O.


(iii) Reducing character decreases from SO2 to TeO2.


(b) Draw the structures of the following:


(i) H4P2O7 (Pyrophosphoric acid)


(ii) XeF2


OR


(a) Draw the structures for the following:


(i) XeF4


(ii) H2S2O7


(b) Account for the following:


(i) Iron on reaction with HCl forms FeCl2 and not FeCl3.


(ii) HClO4 is a stronger acid than HClO.


(iii) BiH3 is the strongest reducing agent amongst all the hydrides of group 15.


 26

(a) Illustrate the following reactions giving suitable examples in each case:

(i) Ammonolysis


(ii) Coupling reaction


(iii) Acetylation of amine


(b) Describe Hinsberg method for the identification of primary, secondary and tertiary amines. Also write the chemical equations of the reactions involved.


OR


(a) Write the structure of main products when benzene diazonium chloride (C6H5Cl-) reacts with the following reagents:


i. HBF4 /Δ


ii. Cu/HBr


(b) Write the structure of A, B and C in the following reactions: