Class 12 Chemistry - CBSE
Chemical Kinetics
Chemical Kinetics in Class 12 CBSE Chemistry explores the speed or rate of chemical reactions and the factors affecting them, such as concentration, temperature, and catalysts. You will learn how to mathematically express reaction rates using rate laws, determine the order and molecularity of reactions, and understand the Arrhenius equation relating reaction rates to temperature. This chapter is highly scoring and crucial for CBSE board exams, typically carrying about 4 to 6 marks. Expect a mix of direct numerical problems based on first-order kinetics and half-life, along with theoretical questions on activation energy and collision theory.
Start Learning FreeKey Concepts
Rate of a Reaction
The change in concentration of a reactant or product in a given unit of time, expressed in mol L^-1 s^-1.
Rate Law and Rate Constant
An expression that relates the rate of a reaction to the molar concentrations of reactants with each term raised to some power, where the rate constant (k) is specific to a given temperature.
Order of a Reaction
The sum of the powers of the concentrations of the reactants in the rate law expression, which can be zero, fractional, or a whole number.
Molecularity
The number of reacting species colliding simultaneously in an elementary reaction; it is always a whole number and cannot be zero or fractional.
Half-Life of a Reaction
The time taken for the concentration of a reactant to be reduced to exactly half of its initial value.
Arrhenius Equation
An equation that expresses the quantitative relationship between the rate constant and temperature, highlighting the concept of activation energy.
Important Formulas
Board Exam Info
In CBSE Class 12 Chemistry board exams, Chemical Kinetics typically carries 4 to 6 marks. Common question types include numerical problems on first-order reaction half-life, graphical questions involving activation energy, differentiating between order and molecularity, and explaining the effect of catalysts on reaction rates.
Frequently Asked Questions
Can the order of a reaction be negative or fractional?
Yes, unlike molecularity, the experimentally determined order of a reaction can be fractional, zero, or even negative.
What is the difference between order and molecularity?
Order is an experimental quantity that applies to both elementary and complex reactions and can be fractional or zero. Molecularity is a theoretical concept applicable only to elementary reactions and must be a positive integer.
Why does the rate of a reaction decrease as time passes?
As the reaction proceeds, the reactants are consumed, so their concentration decreases, which according to the rate law leads to a lower frequency of effective collisions and a slower reaction rate.
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