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Chemistry Chemical Kinetics Chapter - Chemistry JEE Advanced

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Concepts of Chemistry Chemical Kinetics for JEE Advanced Chemistry

In the field of physical chemistry named reaction kinetics, chemical kinetics is concerned with the speed at which chemical reactions occur.


It contrasts with thermodynamics, which deals with the direction in which a process occurs but does not reveal the rate of the process. 


Chemical kinetics is the study of how experimental conditions affect the pace of a chemical reaction, yielding knowledge on the event's mechanism and transition stages, as well as the development of mathematical models that can also characterize the properties of a chemical reaction.


Chemical Kinetics - Formula and Equations

  1. Rate of Chemical Reaction

Chemical reactions, like any other item moving at a particular speed, have their own set of velocities, also known as the rate of reaction. 

This rate of reaction is defined as the rate at which the product is formed or the rate at which the reactants are consumed with time.

\[\Delta R = R_{2} - R_{1}\]

\[\Delta P = P_{2} - P_{1}\]

\[\Delta t = t_{2} - t_{1}\]

Rate of Reaction = Increase in concentration of P/Time taken = Decrease in concentration of R/Time taken

Hence, Rate of Reaction 

=  \[\frac{\Delta P }{\Delta t }\]  

= \[\frac{-\Delta R }{\Delta t }\] 

  1. Rate Expression and Constant Rate: 

General Reaction = aA + bB → cC + dD

The rate equation is given as follows:

\[kA^{x}B^{y}\]

Where 

The coefficients x and y may or may not be stoichiometric.

k = the rate constant.

The order of the reaction is determined by adding these two components (x+y).

  1. Order of a Reaction

A chemical reaction's rate equation is as follows:

Rate = \[kA^{x}B^{y}\]

k = the rate constant.

  1. Zero-Order Reactions

In a zero-order reaction, the reaction's order is determined by the power at which the reactants' concentration is zero.

The rate equation is written as follows:

\[R = -kt + R_{0}\]

  1. First-Order Reactions

The rate of reaction is related to the first power of the reactants' concentration in a first-order reaction.

The rate equation is written as follows:

\[ \frac{log[R]^{0}}{R} = \frac{k(t_{2} - t_{1})}{2.303} \]

  1. Half-life Reactions

The half-life of a reaction is defined as the time it takes for the concentration of the reactant to vary by half from its original value. It is denoted by \[t_{\frac{1}{2}}\].

\[t_{\frac{1}{2}}\] = \[\frac{0.0693}{k}\].

  1. Arrhenius Equation 

The Arrhenius equation describes the pace of a chemical reaction that is temperature-dependent.

Every 100 degrees of temperature increase, the rate constant doubles in value.

The Arrhenius equation, which is provided below, explains the propensity to rely on the rate of the chemical reaction:

K = \[ \frac{Ae^{-E}_{a}}{RT} \]

Where,

A = the Arrhenius factor

Ea = the activation energy 

R = the gas constant


Factors Influencing Reaction Rates

  1. Concentration of Reactants: According to the collision theory, reactant molecules bump into each other to create products. Increase the concentration of reactants, and you'll have more particles colliding, which speeds up the reaction.

  2. Nature of the Reactants: Different substances have different speeds of reaction. Acid/base reactions, salt formation, and ion exchange are often speedy, while reactions forming covalent bonds to make larger molecules tend to be slower. The strength of bonds in reactant molecules also plays a role.

  3. Physical State of Reactants: Whether a reactant is solid, liquid, or gas matters. In the same phase, like an aqueous solution, thermal motion helps mix things up. In different phases, reactions are limited to where the reactants meet, like the surface of a liquid.

  4. Surface Area of Reactants: If you've got two solids, the particles on the surface participate in the reaction. When you crush a solid into smaller pieces, more particles are exposed, leading to more collisions and a faster reaction.

  5. Temperature: Heat things up, and particles collide more frequently, speeding up the reaction. But depending on whether the reaction is endothermic (absorbs heat) or exothermic (releases heat), increased temperature affects the rate of forward or backward reactions.

  6. Solvent's Role: The nature of the solvent can influence the reaction rate. For example, in a reaction between sodium acetate and methyl iodide, it's faster in organic solvents like DMF (dimethylformamide) because they don't form hydrogen bonds with the reactants.

  7. Catalysts: Catalysts are like reaction maestros. They change the reaction mechanism. Some are promoters, speeding things up, while others, the poisons, slow it down.


All these factors can be precisely quantified, and we can even establish mathematical relationships between them and the rate of reaction. 


JEE Main Chemistry Chapters 2024


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Conclusion

Chemical Kinetics emerges as a crucial and intricate chapter for JEE Advanced preparation. Understanding the intricacies of reaction rates, mechanisms, and influencing factors is pivotal. The diverse array of problems posed in this section not only sharpens problem-solving skills but also serves as a litmus test for a candidate's comprehensive grasp of chemical dynamics. Mastery of Chemical Kinetics not only enhances performance in JEE Advanced but also lays a solid foundation for comprehending advanced concepts in chemistry. Dedication to mastering this chapter is an investment in acing the competitive exam and nurturing a profound understanding of chemical reactions.

FAQs on Chemistry Chemical Kinetics Chapter - Chemistry JEE Advanced

1. State brief history of Chemical Kinetics.

The law of mass action, which asserts that the speed of a chemical reaction is related to the number of reacting components, was first proposed by Peter Waage and Cato Guldberg in 1864, paving the way for the development of chemical kinetics. 


Van 't Hoff was a chemist who published his famous "Études de dynamique chimique" in 1884. He received the Nobel Prize in Chemistry for the first time in 1901, "in honor of the tremendous contributions he has made by the discovery of the rules of chemical dynamics and osmotic pressure in solutions."

2. What are the factors that affect the reaction rate?

  • The rate of reaction varies based on the components involved. Acid/base reactions, salt production, and ion exchange are all examples of quick reactions.

  • The physical state of a reactant (solid, liquid, or gas) is also a significant determinant in the rate of change. Thermal motion brings reactants into touch when they are in the same phase, as in an aqueous solution.

  • Only the particles at the surface of a material can be engaged in a reaction.

  • Collisions of reactant species cause the reactions. The rate at which molecules or ions collide is determined by their concentrations.

  • The rate of a chemical reaction is frequently influenced by temperature. Molecules with more thermal energy are found at higher temperatures.

  • In a gaseous process, increasing the pressure increases the number of collisions between reactants, which speeds up the reaction.

3. What is the application of Chemical Kinetics?

Chemists and chemical engineers can use the mathematical models that explain chemical reaction kinetics to better comprehend and characterize chemical processes including food degradation, microorganism growth, stratospheric ozone decomposition, and biological system chemistry.


Kinetic models can be used to determine the temperature and pressure at which the largest yield of heavy hydrocarbons into gasoline occurs when performing catalytic cracking of heavy hydrocarbons into gasoline and light gas, for example.

4. What are some examples of chemical reactions in our daily life?

In plants, photosynthesis is a chemical reaction in which carbon dioxide and water are converted into food (glucose) and oxygen. It's a significant process since it creates oxygen and provides food for plants and animals.


Combustion reactions occur when you strike a match, ignite a candle, start a bonfire, or light a grill.


Digestion is a multi-step process with thousands of chemical reactions. When you put food in your mouth, water and the enzyme amylase break down sugar and other carbohydrates into simpler molecules.

5. What is the rate constant?

The proportionality constant, which explains the link between the molar concentration of the reactants and the pace of a chemical reaction, is known as the rate constant.


The rate constant, which is also called the response rate constant for the reaction rate coefficient, is shown by the letter k. It is influenced by the ambient temperature.


The following are two methods for calculating rate constant:

  • The Arrhenius equation 

  • The order of the reaction and the molar concentrations of the reactants

6. Illustrate the five kinds of Chemical Reactions.

The five basic types of chemical reactions are 

  1. Combination

  2. Decomposition

  3. Single-replacement 

  4. Double-replacement

  5. Combustion


The observer can place the chemical reaction into the given categories by analyzing the reactants and products of a given reaction.


Many kinds of changes have happened during the time of chemical reactions such as a change in temperature, energy wasted via the process, and so on.

7. What is your opinion about the Rate of Reaction?

We can explain the rate of reaction as the amount at which the concentration is altering or the ratio of change in concentration and change in time.


It is given by: r = \[\frac{\Delta (c)}{\Delta t}\]


Where,


rate = r 


change in concentration = \[\Delta (c)\]


change in time = \[ \Delta t \]

8. Mention a factor that affects the Rate Constant (k).

The factors that are affecting the rate constant are given below: 

  • Increasing the temperature of a reaction generally speeds up the process because the rate constant increases according to the Arrhenius Equation. 

  • With the rising value of T, the value of the exponential part of the equation becomes less negative. This results in an increased value of k.

9. What are the major reasons which cause problems for the Reaction Rate?

The major reasons which cause a problem for the reaction rate are

  1. The concentration of reactants

  2. Temperature

  3. Phase and surface area of reactants

  4. Effect of solvent

  5. Catalyst