NCERT Solutions for Class 12 Chemistry Chapter 4 Chemical Kinetics
NCERT Solutions for Class 12 Chemistry Chapter 4 Chemical Kinetics is the study material that will help students in getting tuned in with the concepts involved in chemical kinetics. Chemical kinetics Class 12 NCERT solutions pdf is helpful for the students of CBSE class 12th. Students aspiring to make a career in the medical or engineering field must practise the Class 12 Chemistry Chapter 4 questions to score well in the board exams as well as various competitive entrance exams.
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Students will be able to understand the rate of chemical reaction, Temperature dependence on the rate of reaction, Arrhenius equation and collision theory of chemical reaction. The chapter given here is to assist the students to understand the lesson in an easy and interesting way. The class 12 Chemistry Chapter 4 solutions are created by subject experts as per the latest CBSE syllabus (2020-21). Students must practise the solutions regularly to prepare effectively for their examinations.
Class 12 NCERT Solutions for Chemical Kinetics
Chemical Kinetics is a branch of chemistry. It deals with the rate of chemical reaction, the factors affecting it, the mechanism of the reaction. Based on the rate of reaction we have 3 types: Instantaneous reactions, Slow reactions and moderately slow reactions. Any chemical reaction that completes in less than 1ps time is called a fast reaction. Any chemical reaction happening for some minutes to some years is called a slow reaction. Intermediate chemical reactions that occur between fast and slow chemical reactions are called moderately slow reactions. This was a brief on Chemical Kinetics.
Subtopics for Class 12 Chemistry Chapter 4 – Chemical Kinetics
The rate of a Chemical Reaction
Factors Influencing the Rate of a Reaction
Dependence of Rate on Concentration
Rate Expression and Rate Constant
Order of a Reaction
Molecularity of a Reaction
Integrated Rate Equations
Zero Order Reactions
Half-Life of a Reaction
Pseudo First Order Reaction
Temperature Dependence of the Rate of a Reaction
Effect of Catalyst Ex 4.6 – Collision Theory of Chemical Reactions.
Class 12 Chemistry NCERT Solutions (Chemical Kinetics) – Important Questions
Q 1. From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.
Dimensions of k=[NO]2Rate=(molL−1)2molL−1s−1=mol2L−2molL−1s−1=Lmol−1s−1
(b) Given rate = k[H2O2][I−]
Therefore, order of the reaction = 2
Dimensions of k=[H2O2][I−]Rate=(molL−1)(molL−1)molL−1S−1=Lmol−1s−1
(c) Given rate = =k[CH3CHO]23
Therefore, the order of reaction = 23
Dimensions of k=[CH3CHO]23Rate=(molL−1)23molL−1s−1=mol23L23molL−1s−1L21mol−21s−1
(d) Given rate = k=[C2H5Cl]
Therefore, order of the reaction = 1
Dimension of k=[C2H5Cl]Rate=molL−1molL−1s−1=s−1
Q 2. For the reaction: 2A+B→A2B is k[A][B]2 with k=2.0×10−6mol−2L2s−1. Calculate the initial rate of the reaction when [A] = 0.1 mol L–1, [B] = 0.2 mol L–1. Calculate the rate of reaction after [A] is reduced to 0.06 mol L–1
Q 4. The decomposition of dimethyl ether leads to the formation of CH4,H2,andCO and the reaction rate is given by Rate=k[CH3OCH3]23
The rate of reaction is followed by an increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, i.e.,
If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?
The decomposition of dimethyl ether leads to the formation of CH4, H2 and CO and the reaction rate is given by Rate = k [CH3OCH3] 3/2 The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, Rate = k p(CH OCH3 )3/2. If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?
If pressure is measured in bar and time in minutes, then
Unit of rate = basmin−1Rate=k(PCH3OCH3)23⇒k=k(PCH3OCH3)23Rate
Therefore, unit of rate constants (k)=bar23barmin−1=bar2−1min−1
Q 5. Mention the factors that affect the rate of a chemical reaction.
The factors which are responsible for the effect in chemical reaction’s rate are:
(b) Presence of a catalyst
(c) The concentration of reactants (pressure in case of gases)
Q 6. A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is (i) doubled (ii) reduced to half ?
Let the concentration of the reactant be [A] = a
Rate of reaction, R=k[A]2=ka2
(a) If the concentration of the reactant is doubled, i.e [A] = 2a, then the rate if the reaction would be
Therefore, the rate of the reaction now will be 4 times the original rate.
(b) If the concentration of the reactant is reduced to half, i.e [A]=21a, then the rate of the reaction would be
Therefore, the rate of the reaction will be reduced to 41th
Q 7. What is the effect of temperature on the rate constant of a reaction? How can this effect of temperature on rate constant be represented quantitatively?
When a temperature of 10∘ rises for a chemical reaction then the rate constant increases and becomes near to double of its original value.
The temperature effect on the rate constant can be represented quantitatively by Arrhenius equation,
k = rate constant,
A = Frequency factor / Arrhenius factor,
R = gas constant
T = temperature
Ea = activation energy for the reaction.
Q 8. In a pseudo-first-order reaction in water, the following results were obtained:
[Ester]mol / L
Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(a) Avg rate of reaction between the time intervals, 30 to 60 seconds,
Q 9. A reaction is first order in A and second order in B.
(i) Write the differential rate equation.
(ii) How is the rate affected on increasing the concentration of B three times?
(iii) How is the rate affected when the concentrations of both A and B are doubled?
(a) The differential rate equation will be
(b) If the concentration of B is increased three times, then
Therefore, the reaction rat will be increased by 9 times.
(c) When the concentrations of both A and B are doubled,
Therefore, the rate of reaction will increase 8 times.
Q10. In a reaction between A and B, the initial rate of reaction (r0) was measured for different initial concentrations of A and B as given below:
What is the order of the reaction with respect to A and B?
Let the order of the reaction with respect to A be x and with respect to B be y.
Q 17. During the nuclear explosion, one of the products is 90Sr with a half-life of 28.1 years. If 1µg of 90Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 years and 60 years if it is not lost metabolically.