Chemical Kinetics: Class 12 Chemistry NCERT Chapter 4

Characteristics of NCERT Material for Class 12 Chemistry Chapter 4 – Chemical Kinetics 

In the last chapter 3, you learned about Electrochemistry. In this chapter you will learn about Chemical Kinetics. Do you ever wonder how reactions really occur? What are the conditions essential for a reaction to occur? Is it sure that a reaction will occur even after the conditions are satisfied?

 Well, the one word answer to all these questions is Collision Theory. We should understand what the collision hypothesis is and find out about the conditions referenced in the collision hypothesis.

Collision Theory 

Collision hypothesis fundamentally clarifies how reactions happen and why different reactions have different reaction rates. It expresses that: 

Molecules must collide so as to respond. So as to successfully start a reaction, the molecules in the collisions must have adequate vitality to bring about disruptions in the bonds of molecules. An ascent in temperature will make the molecules move quicker and collide all the more overwhelmingly, improving the probability of bond cleavages and revisions incredibly. The reactions containing impartial molecules can’t occur at all until they have obtained the actuation vitality expected to stretch, twist, or distort at least one bond. 

Quick Revision notes

Chemical kinetics: It is the part of chemistry that manages the investigation of reaction rates and their components. 

Rate of reaction: The adjustment in the convergence of reactant (or product) in unit time. The Rate of reaction has mol L-1s-1 as the unit.

A + B → C + D 

Rate of disappearance of
Where d[A] is little change in conc. of ‘An’ and dt is a little time frameRate of disappearance of
Where d[B] is little change in conc. of ‘B’ and dt is a little timespan 

Rate of appearance of
Where d[C] is little change in conc. of ‘C’ and dt is the little timespan
Rate of appearance of 
Where d[D] is little change in conc. of ‘D’ and dt is the little time period 


Rate law or rate condition: The articulation relates the rate of reaction with the centralization of the reactants. The proportionality constant ‘k’ is known as the rate constant. 

Average rate: The rate of reaction estimated over quite a while span.

Average rate

Where is Δx change in fixation and Δt is an enormous timespan. 

Instantaneous rate: The rate of reaction when the average rate is assumed to control over a specific snapshot of time. Momentary rate. .
Where dx is little change in conc, what’s more, dt is the littlest time frame. It is the articulation that relates the rate of reaction with the centralization of the reactants. 

Rate constant: When the centralization of reactants is solidarity, the rate of reaction is known as the rate constant. It is likewise called an explicit reaction rate. 

The constant of proportionality ‘k’ is known as the rate constant. 

Molecularity of a reaction: The complete number of atoms, particles, or molecules of the reactants associated with the reaction is named as its molecularity. It is consistently in the entire number and is never more than three. It can’t be zero.

Order of a reaction: The total of the types (intensity) of the centralization of reactants in the rate law is named the order of the reaction. It tends to be in part. It may very well be zero moreover.  On the off chance that rate law articulation for a reaction is Rate = k [A]x [B]y 

At that point its order of reaction = x + y 

The order can’t be resolved with a given adjusted chemical condition. It very well may be tentatively decided. 

Probability factor or Steric factor

Where ZAB speaks to the collision recurrence of reactants, An and B, speaks to the portion of molecules with energies equivalent to or more noteworthy than Ea. P is known as the likelihood or steric factor. Component of reaction: The grouping of elementary cycles leads to the general stoichiometry of a chemical reaction. 

Activated complex: It is a flimsy intermediate framed between responding molecules. Since it is profoundly flimsy, and it readily changes into the product. 

Rate deciding advance: It is the slowest step in the reaction instrument. The quantity of collisions every second per unit volume of the reaction blend is known as collision recurrence (Z). 


Q: Mention the significant rules altogether for a reaction to happen. 

Solution: The molecules must collide. The molecules must have the right direction; that is, they should collide from the right side.The colliding molecules must collide with energies more noteworthy than or equivalent to the reaction’s initiation vitality.The molecules can be given dynamic vitality as warm vitality to expand the opportunity of bond cleavages. Hence, if all the rules are satisfied, the collision will prompt realization.

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