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WBJEE: Important Questions and Study Notes for Chemical Kinetics

Jan 29, 2018 11:17 IST
    WBJEE 2018: Chemical Kinetics
    WBJEE 2018: Chemical Kinetics

    West Bengal Joint Entrance Examination (WBJEE) is a state level common entrance test organized by West Bengal Joint Entrance Examinations Board for admission to the Undergraduate Level Engineering and Medical Courses through a common entrance test in the State of West Bengal.

    Physical Chemistry is a very important part of Chemistry in the syllabus of WBJEE 2018. About 35% of the questions come from Physical Chemistry in the paper. The numerical problems asked from this part are not so tough. Students have to apply the related formula to find the answer.

    The chapter “Chemical Kinetics” is one of the most important chapters of Physical Chemistry. Engineering aspirants always get 2-3 questions directly from this chapter in the examination.

    In this article, we bring to you the notes of chapter Chemical Kinetics based on the latest syllabus to help students in their preparation for the examination.

    Some of the most important topics of this chapter are rate of chemical reaction, factors affecting rate of reaction, order of reaction, half life of a reaction.

    Students can read the following topics here:

    1. Chemical Kinetics,
    2. Rate of a chemical reaction,
    3. Instantaneous rate of a reaction,
    4. Average rate of a reaction,
    5. Factors affecting rate of a reaction,
    6. Rate expression,
    7. Rate constant,
    8. Order of a reaction,
    9. Integrated rate equations
    • Zero order reactions and
    • First order reactions

    10.  Half life of a reaction and

    11.  Effect of temperature on rate of a reaction

    WBJEE: Important Questions and Preparation Tips – States of Matter

    Important Concepts:

    WBJEE Chemical Kinetics

    • Factors affecting rate of a reaction

    (i) Concentration: At a given temperature, higher the concentration of reactants greater the rate of reaction.

    (ii) Temperature: As the temperature increases rate of chemical reaction also increases.

    (iii) Catalyst: On adding the catalyst the rate of reaction increases.

    WBJEE Chemical Kinetics

    • Order of a Reaction

    (i) In rate equation sum of the exponents, x + y, gives the overall order of a reaction.

    (ii) Order of a reaction can be integer or even a fraction

    (iii) A zero order reaction means that the rate of reaction is independent of the concentration of reactants.

    (iv) Unit of rate constant for different order of reactions can be found out as:

    WBJEE Chemical Kinetics

    • The reaction taking place in a single step is called elementary reactions.
    • When a reaction does not complete in single step but takes sequence of steps then it is called complex reaction.

    WBJEE Chemical Kinetics

    WBJEE: Important Questions and Preparation Tips – Electrochemistry

    Some previous years solved questions are given below:

    Question 1:

    For the reaction A + 2B → C, the reaction rate is doubled if the concentration of A is doubled. The rate is increased by four times when concentrations of both A and B are increased by four times. The order of the reaction is

    (A) 3

    (B) 0

    (C) 1

    (D) 2

    Solution 1:

    Given:

    Rate is doubled when concentration of ‘A’ is doubled.

    Also, rate is quadrupled when concentration of ‘A’ is raised four times. This means that there is no effect on rate of reaction when we raise the concentration of B.

    Order of reaction with respect to A is 1.

    Order of reaction with respect to B is 0.

    Total order of reaction is 1.

    Hence, the correct option is (C).

    WBJEE: Important Questions and Preparation Tips – Solutions

    Question 2:

    The increase in rate constant of a chemical reaction with increasing temperature is (are) due to the fact(s) that

    (A) the number of collisions among the reactant molecules increases with increasing temperature.

    (B) the activation energy of the reaction decreases with increasing temperature.

    (C) the concentration of the reactant molecules increases with increasing temeprature.

    (D) the number of reactant molecules acquiring the activation energy increases with increasing temperature.

    Solution 2:

    The increase in rate constant of a chemical reaction with increasing temperature is due to the facts that:

    (i) the number of collisions among the reactant molecules increases with increasing temperature.

    (ii) the number of reactant molecules acquiring the activation energy increases with increasing temperature.

    Hence, the correct options are (A) and (D).

    WBJEE: Important Questions and Preparation Tips – Basic Concepts of Chemistry

    You can also have a look on the following questions and solutions to check your preparation.

    Question 1:

    The rate of a reaction doubles when its temperature changes from 300 K to 310 K. Activation energy of such a reaction will be (R= 8.314 JK–1 mol–1 and log 2 = 0.301)                              

    (A) 53.6 kJ mol–1                             

    (B) 48.6 kJ mol–1

    (C) 58.5 kJ mol–1                             

    (D) 60.5 kJ mol–1

    Solution 1:

    WBJEE chemical Kinetics S3

    Hence, the correct option is (A).

    WBJEE: Important Questions and Preparation Tips – Atomic Structure

    Question 2:

    A reaction is second order with respect to a reactant. If the concentration of the reactant is   tripled, then the rate of reaction becomes

    (A) 9 times

    (B) 3 times

    (C) 36 times

    (D) no change

    Solution 2:

    Let the concentration of the reactant [A] = a

    Rate of reaction,

    R = k[A]2

       = ka2

    [A] = 3a,

    Rate of the reaction will be,

    R’ = k(3a)2

         = 9ka2

         = 9R

    Hence, the rate of the reaction will increase by 9 times.

    Hence, the correct option is (A).

    Question 3:

    During nuclear explosion one of the products is 90Sr with half-life of 28.1 yr. If 1 µg of 90Sr

    was absorbed in the bones of a newly born body instead of calcium, how much of it will

    remain after 60 yr, if it is not lost metabolically?

    (A) 0.184 µg

    (B) 0.025 µg

    (C) 0.262 µg

    (D) 0.228 µg

    Solution 3:

    UPSEE Chemical Kinetics Solution 2

    Hence, the correct option is (D).

    Question 4:

    UPSEE Chemical Kinetics Question 3

    Solution 4:

    UPSEE Chemical Kinetics Solution 3

    Hence, the correct option is (d).

    Question 5:

    UPSEE Chemical Kinetics Question 3

    Solution 5:

    UPSEE Chemical Kinetics Solution 4

    Hence, the correct option is (a).

    Conclusion:

    Students can easily get familiar with the difficulty level of the paper with the help of previous years’ solved questions given here. Also, students can practice questions given in these notes to track their progress. It will help students in their preparation and save their precious time.

    WBJEE 2018: Notification, Application, Dates, Eligibility, Exam Pattern, Syllabus

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