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NCERT Questions for Class 12 Chemistry Chapter 3 – Chemical Kinetics
In Class 12 Chemistry Chapter 3 – Chemical Kinetics students explores the rates of chemical reactions and factors affecting them. The group of important questions is intended to help students be ready for and comprehend chemical kinetics, a basic concept in chemistry. These questions give students a solid foundation in the subject by addressing a variety of ideas and approaches to problem-solving.
Important Questions with Solutions of Class 12 Chemistry Chapter 3 – Chemical Kinetics
1) Calculate the average reaction rate via units of time in minutes & seconds, where the accumulation of reactant for the reaction R-> P changes the value in 25 mins from 0.03 M to 0.02 M.
Ans – The average rate of reaction = – ∆R/∆t
= 4 x 10-4 Mmin-1
As per seconds, the calculation will be,
The average rate of reaction = (4 x 10-4)/60 = 6.67 x 10-4.
2) Find the effect of temperature on the rate constant.
Ans – A 10º rise in temp can multiply the rate constant. However, the Arrhenius equation expresses the actual temperature dependence of the chemical reaction rate.
k = Ae-Ea/RT
Where A is the Arrhenius factor(the frequency factor), T is temperature, R is the gas constant, and Ea is the activation energy.
3) Decomposition of dimethyl ether produces CH4, H2, and CO with the rate given by Rate = k = [CH3OCH3]3/2. Since the pressure increase in a closed vessel monitors w.r.t the rate of reaction, then the rate can be expressed in partial pressure of dimethyl I ether. It means Rate = k = (PCH3OCH3)3/2. What are the rate and rate constants, if the pressure is calculated in bar and time in mins?
Ans – The rate of H2 production increased.
Rate = k = (PCH3OCH3)3/2
k = Rate/PCH3OCH3
Hence, the unit of rate constants,
= bar(-1/2) min-1
4) Define the factors controlling a chemical reaction rate.
Ans – Many things affect a reaction rate.
Temperature: The rate of reaction depends highly on the temperature. For each 100°C temp increase, the rate of reaction increases 2-3 times.
Nature of the Reactant: The nature of the reactant decides the rate of the reaction. For instance, reactions involving an ionic compound are quicker than a covalent one.
State of the Reactant: The reactions involving solids are slow, gaseous reactions are fast, and those involving liquids are fast.
(rT+10)/ rT = 2 – 3. This proportion is termed the temperature coefficient.
As the temperature increases, the average kinetic energy of the reacting molecules increases and so will the rate of collision. The number of molecules that obtain threshold energy with an increase in temperature gets elevated. Hence, there is an acceleration in the rate of reaction.
Catalyst: The other influencing factor is the presence of a catalyst. Catalysts speed up the rate of reaction in the following manner; increasing the surface area of reaction thus resulting in an unstable intermediate with the substrate, finally offering a lower activation energy alternative pathway.