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Chemical Kinetics - ISC Class 12 Chemistry Questions with Answers, Page 2

65 past-paper questions on Chemical Kinetics from ISC Class 12 Chemistry papers (2027-2018), newest first, in full. Questions 21-40 are on this page, 20 to a page. Tap "Show answer" under a question to see its answer.

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2025 · 3 marks · Short answerOpen: Answer the following: A patient was given a certain amount of iodine-131 as a…
Answer the following:
Figure for this question
(a)
A patient was given a certain amount of iodine-131 as a part of a diagnostic procedure for thyroid disorder. Given that the half-life of radioactive $^{131}\text{I}$ is 8 days, what fraction of the initial $^{131}\text{I}$ would be present in a patient after 32 days if none of it were eliminated through natural body processes?
(b)
The potential energy diagram, for a multistep reaction is given below: (i) Which step will be the rate determining step of the reaction? (ii) Which step is faster $\text{A} \rightarrow \text{B}$ or $\text{B} \rightarrow \text{C}$?

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2025 · 2 marks · Short answerOpen: In the reaction , the rate law is . How will the rate of reaction change if…
In the reaction $2\text{NO} + \text{O}_2 \longrightarrow 2\text{NO}_2$, the rate law is $\text{rate} = k[\text{NO}][\text{O}_2]^2$.
(i)[1.0]
How will the rate of reaction change if $[\text{NO}]$ concentration is doubled and $[\text{O}_2]$ concentration is halved at the same time?
(ii)[1.0]
Write the order of reaction if $[\text{NO}]$ concentration is in large excess.

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2025 · 3 marks · Case basedOpen: The rate of a reaction depends on the concentration of reactants. The rate law…
The rate of a reaction depends on the concentration of reactants. The rate law for a hypothetical reaction $a\text{A} + b\text{B} \longrightarrow c\text{C} + d\text{D}$ is $\text{rate} = k [\text{A}]^x[\text{B}]^y$ where $x$ and $y$ are calculated experimentally and known as order of reaction. In most cases, the mechanism of a reaction is not straight forward but broken down in simple elementary steps. These steps represent the progress of overall reaction at the molecular level.
Read the passage carefully and answer the questions that follow.
(i)[1.0]
What will be the order of reaction if the unit of $k$ is $\text{mol}^{-2}\text{ L}^2\text{ s}^{-1}$?
(ii)[1.0]
State any one difference between order of reaction and molecularity of reaction.
(iii)[1.0]
For the reaction $2\text{A} \longrightarrow \text{B} + \text{C}$, the rate law is $\text{rate} = k[\text{A}]^{3/2}$. What is the order and molecularity of the reaction?

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2025 · 3 marks · NumericalOpen: Following rate data was obtained at 298 K for the reaction : Answer the…
Following rate data was obtained at 298 K for the reaction $\text{A} + \text{B} \longrightarrow \text{C} + \text{D}$: Answer the following questions.
Figure for this question
(i)[1.0]
What is the order of reaction with respect to A and B?
(ii)[1.0]
Calculate the overall order of reaction.
(iii)[1.0]
Calculate the rate of reaction when $[\text{A}] = 0\cdot8\text{ mol L}^{-1}$ and $[\text{B}] = 0\cdot5\text{ mol L}^{-1}$.

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2025 · 3 marks · NumericalOpen: Consider the data given below for the reaction S.No. conc. of [A] conc. of [B]…
Consider the data given below for the reaction $\text{A} + \text{B} \longrightarrow \text{Product}$
S.No.conc. of [A] $\text{mol L}^{-1}$conc. of [B] $\text{mol L}^{-1}$Rate; $\text{mol L}^{-1}\text{sec}^{-1}$
1.$0\cdot1$$0\cdot1$$4\cdot0 \times 10^{-4}$
2.$0\cdot2$$0\cdot2$$1\cdot6 \times 10^{-3}$
3.$0\cdot5$$0\cdot1$$1\cdot0 \times 10^{-2}$
4.$0\cdot5$$0\cdot5$$1\cdot0 \times 10^{-2}$
Answer the following questions.
(i)[1.0]
What is the order of reaction with respect to A and B?
(ii)[1.0]
Calculate the rate constant.
(iii)[1.0]
Determine the reaction rate when the concentration of A and B are $0\cdot2\text{ mol L}^{-1}\text{sec}^{-1}$ and $0\cdot35\text{ mol L}^{-1}\text{sec}^{-1}$ respectively.

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2025 · 1 mark · Assertion-reasonOpen: The half-life of a first order reaction does not depend on initial…

Assertion: The half-life of a first order reaction does not depend on initial concentration of the reactant.

Reason: The initial reaction expression is present in the expression for rate constant.

  • (a)Both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct explanation of Assertion (A).
  • (b)Both Assertion(A) and Reason (R) are correct, but Reason (R) is not the correct explanation of Assertion (A).
  • (c)Assertion (A) is true, but Reason (R) is false.
  • (d)Assertion (A) is false, but Reason (R) is true.

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2025 · 3 marks · Case basedOpen: A plant or any other living being maintains a reasonable balance of C-14…
A plant or any other living being maintains a reasonable balance of C-14 (radioactive carbon) in its tissue during its lifetime. C-14 is used to determine the age of fossils. In the upper atmosphere, neutrons present in the cosmic rays are captured to produce the following nuclear reaction. $_7\text{N}^{14} + {}_0\text{n}^1 \longrightarrow {}_6\text{C}^{14} + {}_1\text{H}^1$ C-14 isotope is circulated in the atmosphere and gets absorbed by living organism during photosynthesis. The ratio of C-14 to C-12 in living being is $1:10^{12}$. Once the living being dies, the level of C-14 in the dead being decreases due to the following reaction. $_6\text{C}^{14} \longrightarrow {}_7\text{N}^{14} + {}_{-1}\text{e}^0 + \gamma\text{ rays}$ The death of the plant brings an end to its tendency to take up C-14. The half-life period of C-14 is 5770 years. By knowing the concentration of C-14 in the living plant and the piece of dead material at a particular time, the age of the material (fossil) can be determined.
Read the passage carefully and answer the questions that follow.
(i)[1.0]
Write the relation between the decay constant and half-life period.
(ii)[1.0]
In a piece of dead wood, the activity or concentration of C-14 is found to be one third of its initial activity. Calculate the age of the old wood.
(iii)[1.0]
The half-life period ($t_{1/2}$) for a first order reaction is 30 minutes. Calculate the time taken to complete $87\cdot5\%$ of the reaction.

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2025 · 3 marks · Short answerOpen: Answer the following questions: Aman and Rohan were working on the kinetics…
Answer the following questions:
Figure for this question
(a)
Aman and Rohan were working on the kinetics involved in decomposition of hydrogen peroxide in the presence of iodide ions. $\text{H}_2\text{O}_2(l) \rightarrow \text{H}_2\text{O} + \frac{1}{2}\text{O}_2(g)$ They both had their respective hypothesis as follows: According to Aman the rate will be affected by changing the concentrations of hydrogen peroxide and iodide ions as iodide ions are involved in the reaction. According to Rohan the rate will only be affected by changing the concentration of hydrogen peroxide. They carried out several experiments to check their respective hypothesis. Their results are shown graphically below: (i) What do you think whose hypothesis is correct and why? (ii) Do you think that the half -life of this reaction will change if concentration of hydrogen peroxide is reduced to half. Give a reason.
(b)
In a chemical reaction, two reactants take part. The rate of reaction is directly proportional to the concentration of one of them and inversely proportional to the concentration of other. What will be the unit of its rate constant if the concentration terms are in mol/L?

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2024 · 3 marks · Short answerOpen: The data in the table given below was obtained in a series of experiments on…
The data in the table given below was obtained in a series of experiments on the rate of the reaction between compounds [A] and [B] at a constant temperature:
ExperimentThe initial concentration of [A] $\text{mol dm}^{-3}$The initial concentration of [B] $\text{mol dm}^{-3}$Initial rate $\text{mol dm}^{-3}\text{ s}^{-1}$
1$0\cdot15$$0\cdot30$$1\cdot10 \times 10^{-4}$
2$0\cdot30$$0\cdot30$$4\cdot40 \times 10^{-4}$
3$0\cdot60$$0\cdot15$$8\cdot80 \times 10^{-4}$
Show how this data can be used to deduce the rate expression for the reaction between [A] and [B].

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2024 · 3 marks · NumericalOpen: The rate constant of a reaction at and are and respectively. Calculate the…
(i)[1.5]
The rate constant of a reaction at $500\text{ K}$ and $700\text{ K}$ are $0\cdot02\text{ sec}^{-1}$ and $0\cdot07\text{ sec}^{-1}$ respectively. Calculate the value of $E_a$. (activation energy)
(ii)[1.5]
A radioactive substance which emits alpha particle follows first order reaction. The half-life period of this radioactive substance is 30 hours. Calculate the fraction in percent (%) of the radioactive substance which remains after 90 hours.

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2024 · 1 mark · Fill inOpen: Choose the appropriate word(s) from the bracket [lead poisoning, zero…
Choose the appropriate word(s) from the bracket [lead poisoning, zero, phosgene, dependent, cancer, independent, diethyl ether, first, ethyl carbonate, ethene]: For a particular reaction, the value of rate constant is $0\cdot05\text{ sec}^{-1}$. The reaction is of ____ order and will be ____ of the initial concentration.

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2024 · 3 marks · Short answerOpen: For the reaction , following data was obtained: Experiment number Initial…
For the reaction $\text{A} + \text{B} \rightleftharpoons \text{Product}$, following data was obtained:
Experiment numberInitial concentration of $[\text{A}]$ ($\text{mol L}^{-1}$)Initial concentration of $[\text{B}]$ ($\text{mol L}^{-1}$)Initial Rate ($\text{mol L}^{-1}\text{ min}^{-1}$)
10·150·15$9\cdot6 \times 10^{-2}$
20·300·15$3\cdot84 \times 10^{-1}$
30·150·30$1\cdot92 \times 10^{-1}$
40·300·30$7\cdot68 \times 10^{-1}$
Calculate the following:
(i)[1.0]
The overall order of the reaction
(ii)[1.0]
The rate law equation
(iii)[1.0]
The value of rate constant

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2024 · 1 mark · Fill inOpen: Fill in the blanks by choosing the appropriate word(s) from those given in the…
Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [decreases, $\text{CN}^-$ ion, activation energy, catalyst, two, $\text{Fe}^{2+}$ ion, carbon, lattice energy, enzyme, five, double, halogen, triple, increases] In the Haber process, iron changes the ____ of reaction while molybdenum increases the efficiency of the ____.

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