NCERT Class 12 Chemistry Chapter 4 Notes Chemical Kinetics- Download PDF Notes

NCERT Class 12 Chemistry Chapter 4 Notes Chemical Kinetics- Download PDF Notes

Edited By Irshad Anwar | Updated on Apr 30, 2024 05:02 PM IST

The chapter, chemical kinetics is the continuation of the NCERT chapter electrochemistry. The NCERT Class 12 Chemistry chapter 4 notes cover a brief outline of the chapter on chemical kinetics. Class 12 chemistry chapter 4 notes also include a brief introduction to the collision theory of chemical reactions. Chemical kinetics notes class 12 also cover the basic equations in Chapter 4. The necessary derivations are not covered in the CBSE Class 12 Chemistry chapter 4 notes. These chemical kinetics Class 12 notes also include some solved examples related to mentioned topics.

The main topics covered in chapter 4 chemistry class 12 notes are the rate of a reaction, factors influencing the rate of reaction, rate constant and rate expression, order of a reaction, molecularity of a reaction, integrated rate equations for first, second, and zero-order reactions, the half-life of a reaction, pseudo-first-order reactions, temperature dependence of a rate of reaction, and the effect of catalyst on the rate of a reaction. Download the CBSE Notes for chemistry class 12 chapter 4 notes PDF to use offline anywhere.

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NCERT Class 12 Chapter 4 Class Notes: Chemical Kinetics

Definition of chemical kinetics : The branch of Chemistry concerned with the study of the rates of chemical reactions, the mechanism by which the reactions proceed, and the factors affecting the rates of the reactions is called Chemical Kinetics.

Rate of a Chemical Reaction

The rate of a reaction can be defined as the change (decrease or increase) in the concentration of a reactant or product in unit time. The rate of a reaction can be given as:

  • Average rate

The average rate of reaction can be defined as the change in the concentration of a reactant or product in a definite time interval (Δt). It is denoted by the symbol <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>a</mi><mi>v</mi></mrow></msub></math>.

Consider a hypothetical reaction:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>Reactant</mi><mo> </mo><mfenced><mi mathvariant="normal">M</mi></mfenced><mo>→</mo><mi>Product</mi><mo> </mo><mfenced><mi mathvariant="normal">N</mi></mfenced><mo> </mo></math>

The rate of disappearance of reactant-

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>a</mi><mi>v</mi></mrow></msub><mo>=</mo><mfrac><mrow><mi>D</mi><mi>e</mi><mi>c</mi><mi>r</mi><mi>e</mi><mi>a</mi><mi>s</mi><mi>e</mi><mo> </mo><mi>i</mi><mi>n</mi><mo> </mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>c</mi><mi>e</mi><mi>n</mi><mi>t</mi><mi>r</mi><mi>a</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo> </mo><mi>o</mi><mi>f</mi><mo> </mo><mi>M</mi></mrow><mrow><mi>T</mi><mi>i</mi><mi>m</mi><mi>e</mi><mo> </mo><mi>t</mi><mi>a</mi><mi>k</mi><mi>e</mi><mi>n</mi></mrow></mfrac></math>

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>a</mi><mi>v</mi></mrow></msub><mo>=</mo><mfrac><mrow><mo>-</mo><mfenced open="[" close="]"><mi>M</mi></mfenced></mrow><mrow><mo>∆</mo><mi>t</mi></mrow></mfrac></math>

Minus sign indicates a decrease in concentration.

The rate of appearance of the product-

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>a</mi><mi>v</mi></mrow></msub><mo>=</mo><mfrac><mrow><mi>I</mi><mi>n</mi><mi>c</mi><mi>r</mi><mi>e</mi><mi>a</mi><mi>s</mi><mi>e</mi><mo> </mo><mi>i</mi><mi>n</mi><mo> </mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>c</mi><mi>e</mi><mi>n</mi><mi>t</mi><mi>r</mi><mi>a</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo> </mo><mi>o</mi><mi>f</mi><mo> </mo><mi>N</mi></mrow><mrow><mo>∆</mo><mi>t</mi></mrow></mfrac></math>

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>a</mi><mi>v</mi></mrow></msub><mo>=</mo><mfrac><mrow><mo>+</mo><mfenced open="[" close="]"><mi>N</mi></mfenced></mrow><mrow><mo>∆</mo><mi>t</mi></mrow></mfrac></math>

  • Instantaneous rate

The instantaneous rate of reaction can be defined as the change in the concentration of a reactant or product at a particular instant of time. It is denoted by the symbol <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>i</mi><mi>n</mi><mi>s</mi><mi>t</mi></mrow></msub></math>.

For an infinitesimally small instant of time Δt → 0,

Therefore,

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>r</mi><mrow><mi>i</mi><mi>n</mi><mi>s</mi><mi>t</mi></mrow></msub><mo>=</mo><mfrac><mrow><mo>-</mo><mo>d</mo><mfenced open="[" close="]"><mi>M</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mo>d</mo><mfenced open="[" close="]"><mi>P</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac></math>

  • The overall rate of reaction

For an overall rate of reaction, the rate of disappearance of any of the reactants (or the rate of appearance of products) is divided by their corresponding stoichiometric coefficients.

Such that for a reaction,

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>aA</mi><mo> </mo><mo>+</mo><mo> </mo><mi>bB</mi><mo> </mo><mo>→</mo><mo> </mo><mi>cC</mi><mo> </mo><mo>+</mo><mo> </mo><mi>dD</mi></math>

The overall rate is given as:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>1</mn><mi>a</mi></mfrac><mfrac><mrow><mo>-</mo><mo>d</mo><mfenced open="[" close="]"><mi>A</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mn>1</mn><mi>b</mi></mfrac><mfrac><mrow><mo>-</mo><mo>d</mo><mfenced open="[" close="]"><mi>B</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mn>1</mn><mi>c</mi></mfrac><mfrac><mrow><mo>+</mo><mo>d</mo><mfenced open="[" close="]"><mi>C</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mn>1</mn><mi>d</mi></mfrac><mfrac><mrow><mo>+</mo><mo>d</mo><mfenced open="[" close="]"><mi>D</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac></math>

Or

<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mo>-</mo><mfenced open="[" close="]"><mi>A</mi></mfenced></mrow><mrow><mi>a</mi><mo>∆</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mo>-</mo><mfenced open="[" close="]"><mi>B</mi></mfenced></mrow><mrow><mi>b</mi><mo>∆</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mo>+</mo><mfenced open="[" close="]"><mi>C</mi></mfenced></mrow><mrow><mi>c</mi><mo>∆</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mo>+</mo><mfenced open="[" close="]"><mi>D</mi></mfenced></mrow><mrow><mi>d</mi><mo>∆</mo><mi>t</mi></mrow></mfrac></math>

Factors Influencing Rate of a Reaction

Major factors that influence the rate of reaction are:

  • Concentration of reactants

  • Temperature

  • Catalyst

  • Rate Law

Concentration of reactants

When the rate of reaction is represented in terms of the concentration of the reactants is known as rate law. It is also known as the rate equation or rate expression.

Consider the following reaction:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>aA</mi><mo> </mo><mo>+</mo><mo> </mo><mi>bB</mi><mo> </mo><mo>→</mo><mo> </mo><mi>cC</mi><mo> </mo><mo>+</mo><mo> </mo><mi>dD</mi></math>

The rate law for this reaction is:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo>∝</mo><msup><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>x</mi></msup><msup><mfenced open="[" close="]"><mi>B</mi></mfenced><mi>y</mi></msup></math>

Where x and y represent order w.r.t to A and B and may or may not be equal to a and b.

The differential form of rate law is:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mo>-</mo><mo>d</mo><mfenced open="[" close="]"><mi>R</mi></mfenced></mrow><mrow><mo>d</mo><mi>t</mi></mrow></mfrac><mo>=</mo><mi>k</mi><msup><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>x</mi></msup><msup><mfenced open="[" close="]"><mi>B</mi></mfenced><mi>y</mi></msup></math>

  • Order of a reaction

The order of the chemical reaction is the summation of powers raised to the concentration of the reactants in the rate law.

For a reaction,

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>aA</mi><mo> </mo><mo>+</mo><mo> </mo><mi>bB</mi><mo> </mo><mo>→</mo><mo> </mo><mi>cC</mi><mo> </mo><mo>+</mo><mo> </mo><mi>dD</mi></math>

The rate law is:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo>∝</mo><msup><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>x</mi></msup><msup><mfenced open="[" close="]"><mi>B</mi></mfenced><mi>y</mi></msup></math>

Therefore, the order of the reaction is x+y.

The order of a reaction can be 0,1,2,3 and fraction.

Order can never be a negative number.

  • Units of rate constant

REACTION

ORDER

UNITS

Zero-order reaction

0

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>m</mi><mi>o</mi><mi>l</mi><mo> </mo><msup><mi>l</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup><mo> </mo><mi>t</mi><mi>i</mi><mi>m</mi><msup><mi>e</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup></math>

First-order reaction

1

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi><mi>i</mi><mi>m</mi><msup><mi>e</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup></math>

Second-order reaction

2

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>l</mi><mo> </mo><mi>m</mi><mi>o</mi><msup><mi>l</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup><mo> </mo><mi>t</mi><mi>i</mi><mi>m</mi><msup><mi>e</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup></math>

Third-order reaction

3

<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>l</mi><mn>2</mn></msup><mo> </mo><mi>m</mi><mi>o</mi><msup><mi>l</mi><mrow><mo>-</mo><mn>2</mn></mrow></msup><mo> </mo><mi>t</mi><mi>i</mi><mi>m</mi><msup><mi>e</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup></math>

Molecularity of a reaction:

The sum total of species reacting or (molecules, atoms, ions) taking part in a chemical reaction is called the molecularity of a reaction.

The reaction can be unimolecular when one reacting species yields product(s).

The reaction can be bimolecular when two reacting species are involved.

The reaction can be trimolecular when three reacting species are involved.

Integrated rate Equations

  • Zero-order reactions

Consider the reaction,

A → P

The rate law of this reaction is given by:

Rate = k[A]0

On integrating the above equation we get,

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>t</mi></msub><mo>=</mo><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><mo>-</mo><mi>k</mi><mi>t</mi></math>

The graph of the above equation can be plotted as:

1644828448034

  • First-order reaction

Consider the reaction,

A → P

The rate law of this reaction is given by:

Rate = k[A]

On integrating the above equation we get,

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ln</mi><mfenced><mfrac><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>t</mi></msub></mfrac></mfenced><mo>=</mo><mi>k</mi><mi>t</mi></math>

The exponential form of a first-order reaction is given as:

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>t</mi></msub><mo> </mo><mo>=</mo><mo> </mo><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><msup><mi>e</mi><mrow><mo>-</mo><mi>k</mi><mi>t</mi></mrow></msup></math>

The following equation can be used to plot graphs of first-order reactions:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mfrac><mn>1</mn><mi>t</mi></mfrac><mi>ln</mi><mfenced><mfrac><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>t</mi></msub></mfrac></mfenced></math>

1644828448531

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>log</mi><mfrac><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mi>t</mi></msub></mfrac><mo>=</mo><mfrac><mrow><mi>k</mi><mi>t</mi></mrow><mrow><mn>2</mn><mo>.</mo><mn>303</mn></mrow></mfrac></math>

1644828448711

The half-life of a reaction:

The time in which the concentration of a reactant is decreased to one-half of its initial concentration is known as the half-life of a reaction. Half-life is represented as t1/2.

  • For zero-order reactions

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>t</mi><mfrac bevelled="true"><mn>1</mn><mn>2</mn></mfrac></msub><mo>=</mo><mfrac><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub><mrow><mn>2</mn><mi>k</mi></mrow></mfrac></math>

  • For first-order reactions

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>t</mi><mfrac bevelled="true"><mn>1</mn><mn>2</mn></mfrac></msub><mo>=</mo><mfrac><mrow><mn>0</mn><mo>.</mo><mn>693</mn></mrow><mi>k</mi></mfrac></math>

Note that for zero-order reaction <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>t</mi><mfrac bevelled="true"><mn>1</mn><mn>2</mn></mfrac></msub><mo>∝</mo><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub></math>. For the first-order reaction, <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>t</mi><mfrac bevelled="true"><mn>1</mn><mn>2</mn></mfrac></msub></math> is independent of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mfenced open="[" close="]"><mi>A</mi></mfenced><mn>0</mn></msub></math>.

Pseudo-first-order reactions:

The reactions in which the actual order is different from the expected rate order predicted using rate law are called pseudo-first-order reactions.

<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>CH</mi><mn>3</mn></msub><msub><mi>COOC</mi><mn>2</mn></msub><msub><mi mathvariant="normal">H</mi><mn>5</mn></msub><mo> </mo><mo>+</mo><mo> </mo><msub><mi mathvariant="normal">H</mi><mn>2</mn></msub><mi mathvariant="normal">O</mi><mo> </mo><mover><mo>→</mo><msup><mi mathvariant="normal">H</mi><mo>+</mo></msup></mover><msub><mi>CH</mi><mn>3</mn></msub><mi>COOH</mi><mo> </mo><mo>+</mo><mo> </mo><msub><mi mathvariant="normal">C</mi><mn>2</mn></msub><msub><mi mathvariant="normal">H</mi><mn>5</mn></msub><mi>OH</mi><mspace linebreak="newline"></mspace></math>

The rate law of the reaction:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo>=</mo><msup><mi>k</mi><mo>'</mo></msup><mfenced open="[" close="]"><mrow><mi>C</mi><msub><mi>H</mi><mn>3</mn></msub><mi>C</mi><mi>O</mi><mi>O</mi><msub><mi>C</mi><mn>2</mn></msub><msub><mi>H</mi><mn>5</mn></msub></mrow></mfenced><mfenced open="[" close="]"><mrow><msub><mi>H</mi><mn>2</mn></msub><mi>O</mi></mrow></mfenced></math>

Expected order = 2

The concentration of water does not get altered much during the reaction as it is in excess and can be considered constant.

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo>=</mo><mi>k</mi><mfenced open="[" close="]"><mrow><mi>C</mi><msub><mi>H</mi><mn>3</mn></msub><mi>C</mi><mi>O</mi><mi>O</mi><msub><mi>C</mi><mn>2</mn></msub><msub><mi>H</mi><mn>5</mn></msub></mrow></mfenced></math>

Actual order = 1

Therefore, the reaction behaves as a first-order reaction, and such reactions are called pseudo-first-order reactions.

Temperature Dependence of the Rate of a Reaction

The fact that the rate of a chemical reaction is dependent on temperature can be explained by the Arrhenius equation.

The mathematical form of the Arrhenius equation is given below:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mi>A</mi><msup><mi>e</mi><mfrac bevelled="true"><mrow><mo>-</mo><mi>E</mi><mi>a</mi></mrow><mrow><mi>R</mi><mi>T</mi></mrow></mfrac></msup></math>

where A is the Arrhenius factor / the frequency factor / the pre-exponential factor.

According to Arrhenius, a reaction can take place only when two (or more) molecules collide to form an unstable intermediate. This intermediate exists for a very short time and then breaks up to form product(s).

1644828450009

The activation energy (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>E</mi><mi>a</mi></msub></math>) is the mandatory energy required to produce the intermediate activated complex (C). The reaction coordinate depicts the energy change profile when reactants change into products.

The minimum energy which the colliding molecules required to collide effectively is called threshold energy.

Threshold energy = Activation energy + Energy of the reactants

1644828450204

The rate of reaction depends on the temperature as it is found that with the rise in temperature by 10°, the rate constant is nearly doubled.

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>T</mi><mi>e</mi><mi>m</mi><mi>p</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>t</mi><mi>u</mi><mi>r</mi><mi>e</mi><mo> </mo><mi>c</mi><mi>o</mi><mi>e</mi><mi>f</mi><mi>f</mi><mi>i</mi><mi>c</mi><mi>i</mi><mi>e</mi><mi>n</mi><mi>t</mi><mo> </mo><mo>=</mo><mfrac><mrow><mo> </mo><mo>(</mo><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo> </mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>s</mi><mi>tan</mi><mi>t</mi><mo> </mo><mi>a</mi><mi>t</mi><mo> </mo><mi>T</mi><mo> </mo><mo>+</mo><mo> </mo><msup><mn>10</mn><mi>o</mi></msup><mo> </mo><mo>)</mo><mo> </mo><mo> </mo></mrow><mrow><mo>(</mo><mi>R</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo> </mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>s</mi><mi>tan</mi><mi>t</mi><mo> </mo><mi>a</mi><mi>t</mi><mo> </mo><msup><mi>T</mi><mi>o</mi></msup><mo> </mo><mo>)</mo></mrow></mfrac></math>

At a particular temperature, the fractions of molecules are plotted against corresponding kinetic energies, a graph given below is obtained.

The peak of the curve represents the kinetic energy possessed by the maximum fraction of molecules and is called the most probable kinetic energy.

1644828450827

Here, the yellow area shows the fraction of additional molecules which react at t+10 while the grey area shows the fraction of molecules reacting at t.

Taking ln on both sides of the following equation:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mi>A</mi><msup><mi>e</mi><mfrac bevelled="true"><mrow><mo>-</mo><mi>E</mi><mi>a</mi></mrow><mrow><mi>R</mi><mi>T</mi></mrow></mfrac></msup></math>

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ln</mi><mfenced><mi>k</mi></mfenced><mo>=</mo><mfrac><mrow><mo>-</mo><msub><mi>E</mi><mi>a</mi></msub></mrow><mrow><mi>R</mi><mi>T</mi></mrow></mfrac><mo>+</mo><mi>ln</mi><mfenced><mi>A</mi></mfenced></math>

Arrhenius equation for two different temperatures can be modified as:

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>log</mi><mfrac><msub><mi>k</mi><mn>2</mn></msub><msub><mi>k</mi><mn>1</mn></msub></mfrac><mo>=</mo><mfrac><msub><mi>E</mi><mi>a</mi></msub><mrow><mi>R</mi><mi>T</mi></mrow></mfrac><mfrac><mfenced open="[" close="]"><mrow><msub><mi>T</mi><mn>2</mn></msub><mo>-</mo><msub><mi>T</mi><mn>1</mn></msub></mrow></mfenced><mrow><msub><mi>T</mi><mn>1</mn></msub><msub><mi>T</mi><mn>2</mn></msub></mrow></mfrac></math>

Effect of Catalyst:

  • A catalyst is a substance that alters or changes the rate of a reaction without undergoing any permanent chemical change.

  • According to intermediate complex theory, a catalyst forms temporary bonds with the reactants, forming an intermediate complex. This is how a catalyst participates in a chemical reaction.

  • The catalyst reduces the energy difference known as activation energy between products and reactants which in turn lowers the potential energy barrier.

  • A catalyst catalyses to the same extent the forward as well as the backward reactions so that the equilibrium state remains same but equilibrium is reached faster.

1644828451210

Collision Theory of Chemical Reactions

  • According to the collision theory of chemical reactions, the reactant molecules are supposed as hard spheres, and the reaction takes place when molecules collide with each other.

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mo>+</mo><mi>B</mi><mo>→</mo><mi>P</mi><mi>r</mi><mi>o</mi><mi>d</mi><mi>u</mi><mi>c</mi><mi>t</mi><mi>s</mi></math>

  • The collision frequency (Z) can be defined as the number of collisions per second per unit volume of the reaction mixture.
  • Activation energy also affects the rate of chemical reactions.
  • Only effective collisions lead to the formation of products.
  • The proper orientation of reactant molecules in space leads to bond formation whereas due to improper orientation no products are formed.
  • The factor for proper orientation during effective collisions is called the probability or steric factor (P).

<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo> </mo><mo>=</mo><mo> </mo><mi>P</mi><msub><mi>Z</mi><mrow><mi>A</mi><mi>B</mi></mrow></msub><msup><mi>e</mi><mrow><mo>-</mo><mfrac bevelled="true"><msub><mi>E</mi><mi>a</mi></msub><mrow><mi>R</mi><mi>T</mi></mrow></mfrac></mrow></msup></math>

Chapter-Wise NCERT Class 12 Notes Chemistry

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Chemical kinetics Class 12 notes will be helpful to revise the chapter and get an idea about the main topics covered in the chapter. Also, this NCERT Class 12 Chemistry chapter 4 notes are useful to cover the main topics of Class 12 CBSE Chemistry Syllabus and also for competitive exams like VITEEE, BITSAT, JEE Main, NEET, etc. Class 12 Chemistry chapter 4 notes PDF download can be used to prepare in offline mode.

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Frequently Asked Questions (FAQs)

1. 1. How many derivations are covered in chemical kinetics Class 12 notes?

Ans- This NCERT Class 12 Chemistry chapter 4 notes is brief short notes of the main topics. None of the derivations are covered in the NCERT notes for Class 12 Chemistry chapter 4. The equations covered in the chapter and can be used for revising the chemical kinetics.

2. 2. In ncert Class 12 Chemistry chapter 4, what are the main derivations?

Ans- The main derivations covered in the NCERT book (Link) are integrated zero-order reaction, integrated first-order reaction, the half-life of a reaction, Arrhenius equation, etc.

3. 3. How important is the chapter for the CBSE board exam (Link)?

Ans- Students can expect 4 to 6 mark questions (including numerical questions) from the chapter chemical kinetics.

4. 4. Write the unit of a first-order reaction rate constant.

Ans- Students can expect 4 to 6 mark questions (including numerical questions) from the chapter chemical kinetics.

5. 5. State the first order reaction equation in exponential form.

Ans- Students can expect 4 to 6 mark questions (including numerical questions) from the chapter chemical kinetics.

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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