Chemical Kinetics is a chapter in the CBSE Class 12 Chemistry syllabus from Chemistry - I. This chapter hub brings together revision notes, practice questions, worksheets, flashcards, formula sheet to help students learn, practice, and revise Chemical Kinetics effectively.

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Chemical Kinetics

NCERT Class 12 Chemistry Chapter 3: Chemical Kinetics (Pages 61–88)

Class 12 CBSE hub Chemistry chapters Chemistry - I

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Summary of Chemical Kinetics

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Chemical Kinetics at a Glance

Board

CBSE

Class

Class 12

Subject

Chemistry

Book

Chemistry - I

Chapter

Pages

61–88

Resources

7 study resources

Chemical Kinetics Summary

Chemical kinetics is the area of chemistry that studies how fast chemical reactions occur and what factors affect these rates. The understanding of reaction rates is central to many practical applications, including improving the shelf-life of food, optimizing combustion in engines, and designing effective pharmaceuticals. The chapter begins by explaining the basic concepts of reaction rates, which can be understood as the change in concentration of reactants or products over time. This might involve understanding how quickly a substance is consumed during a reaction or how fast a product forms. To delve deeper, the chapter differentiates between average and instantaneous rates. The average rate gives a broader view over a period, while the instantaneous rate focuses on a specific moment during the reaction. Both are essential for a thorough understanding of kinetics. The chapter also categorizes reactions based on their speed, distinguishing between rapid reactions, like the precipitation reactions that occur almost instantaneously, and very slow reactions, such as rusting. Understanding the speed of these reactions can help predict and control them in various settings. Essential concepts such as the effect of concentration, temperature, and catalysts on reaction rate are covered extensively since these factors can significantly alter reaction dynamics. For instance, increasing the concentration of reactants typically increases the rate of a reaction, while temperature variations can lead to differing rates due to increased kinetic energy at higher temperatures. The chapter provides a mathematical foundation through the rate law and its expression, with particular emphasis on determining the reaction order experimentally. It walks students through the concept of molecularity versus order, crucial in understanding intricate reaction mechanisms. Furthermore, it introduces the concept of the activated complex and activation energy through the Arrhenius equation, explaining how temperature influence reaction rates. In addition to these foundational explanations, the chapter explores collision theory, explaining how molecular collisions result in chemical reactions, highlighting the importance of proper orientation and energy. This thorough overview will equip students with the necessary insights to explore chemical kinetics more deeply in future studies.

Chemical Kinetics Revision Guide

Download the Chemical Kinetics revision guide with key points, summaries, and quick revision notes for CBSE Class 12 Chemistry.

Key Points

Rate of reaction: Definition and units.

Rate of reaction refers to the change in concentration of reactants or products per unit time, expressed as mol L^-1 s^-1.

Average and instantaneous rates.

Average rate is calculated over a time interval, while instantaneous rate is the slope of the tangent at a specific time.

Units of rate constant (k).

For zero order: mol L^-1 s^-1; first order: s^-1; second order: L mol^-1 s^-1.

Rate law and expression.

Rate law relates reaction rate to reactant concentrations. It must be determined experimentally.

Reaction order: Definition.

Order refers to the sum of the powers of concentration of reactants in the rate expression.

Molecularity vs. order.

Molecularity is a count of the reacting species in an elementary step, while order can be fractional or zero.

Zero-order reactions.

Rate is constant and independent of reactant concentration. k = [R]0 - [R] = kt.

First-order reactions.

Rate depends on one reactant's concentration. Integrated form: ln[R] = -kt + ln[R]0.

Half-life of zero-order: t1/2.

For zero-order, t1/2 = [R]0 / (2k). It is dependent on initial concentration.

Half-life of first-order: t1/2.

For first-order, t1/2 = 0.693 / k. It is independent of initial concentration.

Temperature effects on rate.

Increasing temperature generally increases reaction rates. Arrhenius equation: k = Ae^(-Ea/RT).

Collision theory overview.

Collision theory states molecules must collide with proper orientation and energy to react.

Factors affecting reaction rates.

Concentration, temperature, catalysts, and pressure (for gases) influence rates.

Catalysts: Definition and role.

Catalysts increase reaction rates without being consumed, by lowering activation energy.

Activated complex and Ea.

The activated complex is a transient state during the formation of products, requiring activation energy (Ea).

Differential vs. integrated rate equations.

Differential equations express rate directly. Integrated equations relate concentration to time.

Pseudo first-order reactions.

In reactions with one reactant in large excess, the rate appears first-order with respect to the other.

Hydrolysis as example of kinetics.

Hydrolysis reactions demonstrate pseudo first-order kinetics when water is in excess.

Rate constant dependence.

Rate constants change with temperature and are specific to reactions; higher temperatures yield larger k values.

Applications of kinetics.

Understanding kinetics allows predictions in various fields like pharmaceuticals, food preservation, and environmental science.

Common misconceptions.

Assuming molecularity equals order; order determined experimentally cannot be inferred from the balanced equation.

Chemical Kinetics Practice Questions & Answers

Practice important questions and exam-style problems from Chemical Kinetics. These questions cover key topics from the CBSE Class 12 Chemistry syllabus.

How to practice: Start with the questions below to test your understanding of Chemical Kinetics. Use the revision guide to review concepts you find difficult, then come back and retry the questions for better retention.

What is the order of a reaction if the rate law is expressed as rate = k[A]^2?

Single Answer MCQ

Q-00083233

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If the rate constant k for a first-order reaction is 3.0 s^-1, what is the half-life of the reaction?

Single Answer MCQ

Q-00083234

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In a zero-order reaction, how does the rate change as the concentration of reactants decreases?

Single Answer MCQ

Q-00083235

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Which of the following statements about first-order reactions is true?

Single Answer MCQ

Q-00083236

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Given a reaction with a rate law of rate = k[A][B]^2, what is the overall order of the reaction?

Single Answer MCQ

Q-00083237

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If the initial rate of reaction is 0.1 mol L^-1 s^-1 when [A]=0.2 mol L^-1 and [B]=0.1 mol L^-1, what is the rate constant k for the reaction A + 2B → products?

Single Answer MCQ

Q-00083238

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What type of reaction is represented if the rate of reaction is independent of the concentration of reactants?

Single Answer MCQ

Q-00083239

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In a first-order reaction, if the time taken for the concentration to decrease from 0.8 M to 0.4 M is 30 minutes, what is the rate constant k?

Single Answer MCQ

Q-00083240

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View all 114 Chemical Kinetics questions

If a plot of ln[R] vs. time (t) gives a straight line, how can we classify the reaction order?

How does increasing temperature typically affect the rate constant k for a chemical reaction?

What is the term used to describe the time required for the concentration of a reactant to decrease to half its initial value in a first-order reaction?

If the half-life of a first-order reaction is doubled, how does the rate constant change?

Which of the following processes follows first-order kinetics?

What does the slope of the plot of ln[R] versus time represent in first-order kinetics?

What does the rate of a chemical reaction indicate?

In which scenario will the rate of reaction typically increase?

Which of the following is the correct formula for the average rate of a chemical reaction?

Which of the following factors does NOT affect the rate of reaction?

For the reaction 2A + B -> A2B, if the rate equation is given by rate = k[A][B]^2, what is the overall order of the reaction?

What is the effect of increasing a catalyst on a reaction?

If the concentration of one reactant is doubled in a second-order reaction, how does the reaction rate change?

For a reaction with rate constant k, if the temperature increases, what is likely to happen to the value of k according to the Arrhenius equation?

What is the rate of a zero-order reaction dependent on?

If a reaction slows down over time, which type of reaction is most likely occurring?

What is the relationship between pressure and rate of reaction for gaseous reactants at constant temperature?

Which of the following is NOT included when discussing factors affecting reaction rates?

How is the instantaneous rate of reaction defined?

If a reaction's rate constant (k) is affected by temperature, which law can be applied to describe this relationship?

For a reaction with an activation energy (Ea) of 50 kJ/mol, what happens to the reaction rate if Ea is increased?

When calculating the rate of a complex reaction, which method is typically used?

Which of the following factors increases the rate of a chemical reaction?

What is the effect of a catalyst on a chemical reaction?

How does temperature affect reaction rates?

In the context of reaction rates, what does the term 'activation energy' refer to?

Which reaction is likely to occur fastest according to typical reaction rate principles?

When the concentration of reactants decreases, how is the average rate of a reaction affected?

What effect does increasing the surface area of a solid reactant have on the reaction rate?

The rate of a reaction is measured in units of:

What is the term for the time it takes for the concentration of a reactant to decrease by half?

Which statement is true about enzyme-catalyzed reactions?

Which type of collision is most effective in leading to a chemical reaction?

At what temperature will most reactions occur at a noticeably faster rate?

How is a reaction rate affected if the pressure of gaseous reactants is increased?

In a chemical reaction, what does it mean if the rate remains constant over time?

If the rate of a reaction is doubled when the concentration of reactants is tripled, what is the order of the reaction with respect to those reactants?

What is the half-life of a first-order reaction?

For a zero-order reaction, how does the half-life relate to the initial concentration?

The rate law for a reaction is Rate = k[A][B]^2. What is the overall order of the reaction?

A first-order reaction has a rate constant k = 3.0 × 10^-3 s^-1. What is the half-life of this reaction?

Which of the following gives the correct relationship between half-life and rate constant for first-order reactions?

What is the effect of changing the initial concentration on the half-life of a first-order reaction?

If a reaction exhibits zero-order kinetics, which of the following statements is true?

For a reaction with rate = k[A]^2[B], what dimensions does the rate constant k have?

In a first-order reaction, which statement is true regarding time for 99.9% completion?

The term 'rate law' refers to which of the following?

If the concentration of a reactant is doubled in a first-order reaction, what happens to the rate?

For the reaction A → B, what does a zero-order reaction imply about the rate?

If a reaction's rate constant decreases, what happens to the reaction rate for a zero-order reaction?

Calculate the initial rate of reaction given k = 2.0 × 10^-6 mol^-2 L^2 s^-1 for [A] = 0.1 mol L^-1 and [B] = 0.2 mol L^-1 with the rate law Rate = k[A][B]^2.

What defines a zero-order reaction?

Which of the following is the integrated rate law for a first-order reaction?

If the rate constant 'k' of a zero-order reaction is 0.5 M/s, how long will it take for the reactant concentration to decrease from 2.0 M to 1.0 M?

A reaction has a rate constant of 0.05 s⁻¹. What is the half-life of the reaction if it follows first-order kinetics?

For the reaction A → products, the rate law is given as rate = k[A]². What is the overall order of the reaction?

During a zero-order reaction, when the concentration of reactant A decreases from 3.0 M to 1.5 M, what does this imply about the reaction rate?

Which of the following factors does NOT affect the rate of a zero-order reaction?

An integrated rate law for a first-order reaction shows a linear plot when plotted against what variable?

Which of the following statements about the integrated rate equations is TRUE for zero-order reactions?

If the rate of formation of product P from reactant R is 0.02 M/s, what is the rate of disappearance of R if the stoichiometry of the reaction is R → P?

For the reaction 2A → B, if the concentration of A is tripled, how does it affect the rate if the reaction is second-order with respect to A?

Which of the following describes the effect of temperature on reaction rates generally?

What is a characteristic feature of elementary reactions compared to complex reactions?

What happens to the rate of a chemical reaction when the temperature is increased?

According to the Arrhenius equation, what effect does increasing the activation energy have on the rate constant?

If the rate constant of a reaction at 300 K is k, what happens to k if the temperature is increased to 310 K?

At what temperature increase is the rate constant approximately doubled for many chemical reactions?

Which of the following statements about the Maxwell-Boltzmann distribution is true when the temperature of a gas increases?

In the context of chemical kinetics, what is represented by the term 'activation energy' (Ea)?

Which of the following factors can increase the rate of a reaction, according to collision theory?

What is the effect of a catalyst on the activation energy of a reaction?

In a pseudo-first order reaction, what is the role of one of the reactants being in excess?

Consider a reaction with a temperature increase from 25 °C to 35 °C. If the rate doubles, what can be inferred about its activation energy?

What is the primary reason for the increased reaction rate with increased temperature?

In the context of temperature's effect on reaction rates, what does the term 'rate constant' refer to?

What happens to the potential energy of molecules as temperature rises?

How does the presence of a catalyst differ from temperature changes regarding activation energy?

If a chemical reaction has a rate constant of 3.5 × 10^-3 s^-1 at 298 K, how would the rate constant change if the temperature is raised to 308 K, assuming classic Arrhenius behavior?

What is the primary assumption of collision theory?

Which of the following factors is most crucial for a collision to be classified as effective?

What term describes the number of collisions per second per unit volume in a reaction mixture?

Activation energy can be defined as:

According to collision theory, what primarily increases the reaction rate?

What is the term for collisions that lead to product formation?

If the rate of a reaction doubles when the temperature is increased by 10 K, which statement is true regarding activation energy?

The probability of a successful collision increases when:

Which of the following best describes the steric factor in collision theory?

Effective collision requires that colliding molecules have:

Which of the following statements is true about the factors affecting reaction rates?

What distinguishes a zero-order reaction from a first-order reaction in terms of collision theory?

Which type of reaction mechanism can be explained by collision theory?

What is a catalyst?

How does a catalyst affect the activation energy of a reaction?

Which of the following statements is true about catalysts?

What is the main effect of increasing the temperature on catalyzed reactions?

Which theory explains the action of catalysts through the formation of intermediate complexes?

In a reaction where the presence of a specific catalyst accelerates the reaction rate, what can be said about the pathway taken by the reaction?

Which of the following is an example of a catalyst?

What does the term 'rate constant' refer to in the context of catalyzed reactions?

Which of the following examples describes heterogeneous catalysis?

In a reaction where a catalyst is removed after the reaction, which of the following can occur?

What happens to the rate constant and activation energy when a catalyst is added to a reaction?

What is the role of temperature in catalytic reactions?

In terms of reaction mechanisms, what does a catalyst primarily influence?

Why do catalysts not appear in the overall reaction equation?

Single Answer MCQ

Q-00083346

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Chemical Kinetics Practice Worksheets

Download and practice Chemical Kinetics worksheets to improve problem-solving accuracy and speed for CBSE Class 12 Chemistry exams.

Chemical Kinetics - Practice Worksheet

This worksheet covers essential long-answer questions to help you build confidence in Chemical Kinetics from Chemistry - I for Class 12 (Chemistry).

Practice

Questions

Define the average and instantaneous rates of a reaction. How would you calculate each in a given reaction?

The average rate of a reaction is defined as the change in concentration of a reactant or product over a specific time period. Mathematically, it can be expressed as: Average Rate = Δ[Reactant]/Δt or Δ[Product]/Δt. The instantaneous rate, on the other hand, refers to the rate at a specific moment in time, which can be determined by taking the slope of the tangent to the concentration vs. time curve at that point. For a reaction A -> B, you would differentiate the concentration with respect to time.

What factors affect the rate of a chemical reaction? Explain how each factor influences the reaction rate.

The rate of a chemical reaction can be influenced by several factors: 1) Concentration: Increasing the concentration of reactants generally leads to a higher rate due to more frequent collisions. 2) Temperature: Raising the temperature typically increases reaction rates as it provides reactant molecules with more kinetic energy. 3) Surface Area: For solid reactants, increasing the surface area (e.g., using powdered solids) allows more collisions to occur, enhancing the rate. 4) Catalyst: A catalyst lowers the activation energy of reactions, increasing the rate without being consumed. For example, the use of MnO2 speeds up reactions such as KClO3 decomposition.

Differentiate between the order and molecularity of a reaction. Give examples of each.

Order of a reaction refers to the power to which the concentration of a reactant is raised in the rate law equation, and it is determined experimentally. For example, for the reaction rate = k[A]^2[B], the order is 3 (2 for A and 1 for B). Molecularity, on the other hand, refers to the number of reacting species in an elementary step of a reaction. For example, in the reaction A + B → products, the molecularity is 2 (bimolecular). A reaction can be first-order, second-order, etc., but its molecularity is usually whole numbers like 1, 2, or 3.

Explain the collision theory of chemical reaction rates. How does it relate to activation energy?

Collision theory states that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation. The rate of a reaction is proportional to the number of effective collisions. Activation energy (Ea) is the minimum energy required for a collision to result in a chemical reaction. The higher the activation energy, the fewer molecules possess enough energy to react at a given temperature, resulting in a slower reaction rate. Thus, increasing temperature increases the fraction of molecules with energy greater than Ea, enhancing the reaction rate.

What is the Arrhenius equation, and how does it relate temperature to the rate constant?

The Arrhenius equation is expressed as k = Ae^(-Ea/RT), where k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the universal gas constant, and T is the temperature in Kelvin. This equation shows that the rate constant increases exponentially with an increase in temperature, as higher temperatures provide more molecules with sufficient energy to overcome the activation energy barrier. This relationship highlights the temperature dependence of reaction rates.

Define the term 'rate constant' and explain how it is determined for zero and first-order reactions.

The rate constant (k) is a proportionality factor that relates the rate of a reaction to the concentrations of reactants in the rate law. For a zero-order reaction, the integrated rate law is [A] = [A]0 - kt, and k can be calculated as k = [A]0/t when concentration decreases linearly over time. For a first-order reaction, the relationship is ln[A] = ln[A]0 - kt. Here, k can be determined from a plot of ln[A] vs. time, where the slope of the line is -k.

What role do catalysts play in chemical reactions? Provide an example.

Catalysts increase the rate of a reaction by lowering the activation energy, ensuring that more collisions result in reactions without being consumed in the process. An example is the use of Enzymes (biological catalysts) in metabolic reactions, like catalase which decomposes hydrogen peroxide into water and oxygen. In industrial processes, catalysts like platinum are used to speed up reactions during the oxidation of hydrocarbons to produce carboxylic acids.

Explain the significance of determining the order of a reaction. How is it experimentally established?

Determining the order of a reaction is significant as it influences the rate law equation, which informs how changes in reactant concentrations will affect the reaction rate. The order can be experimentally established through methods such as the initial rates method, where initial rates are measured for different concentrations of reactants, or the integrated rate laws, where plots of concentration versus time reveal the reaction order based on the linearity of the data. For example, if a plot of ln[A] vs. time yields a straight line, the reaction is first order in A.

How do temperature changes affect the rate constant of a reaction and provide mathematical justification?

Temperature changes typically affect the rate constant (k) of a reaction, increasing it with higher temperatures due to the greater number of molecules having energy exceeding the activation energy. This is described mathematically by the Arrhenius equation: k = Ae^(-Ea/RT). As T increases, the term e^(-Ea/RT) increases, resulting in a higher k. For example, an increase in temperature can nearly double the rate constant for many reactions, demonstrating the exponential relation between k and T.

Chemical Kinetics - Mastery Worksheet

This worksheet challenges you with deeper, multi-concept long-answer questions from Chemical Kinetics to prepare for higher-weightage questions in Class 12.

Mastery

Questions

Explain the concept of reaction rate and provide the equations that define average and instantaneous rates. Illustrate the differences with a diagram showing how these rates change over time.

The reaction rate is defined as the change in concentration of reactants or products per unit time. Average rate is measured over a finite time interval, while instantaneous rate is the rate at a specific moment. The equations are \( r_{av} = -\frac{\Delta [R]}{\Delta t} \) and \( r_{inst} = -\frac{d[R]}{dt} \). A diagram can depict how concentration changes over time, showing slopes of secant and tangent lines.

Discuss the factors affecting the rate of a chemical reaction, and illustrate each factor with relevant examples from real-life scenarios.

Factors include concentration (higher concentration typically increases rate), temperature (increased temperature usually accelerates reactions), and the presence of catalysts (which lower activation energy). For example, food spoilage is accelerated by higher temperatures and microbial concentration.

Differentiate between molecularity and order of a reaction. Provide examples to clarify your distinctions.

Molecularity refers to the number of reactant particles involved in a single elementary reaction and can be 1, 2, or 3. For instance, the unimolecular decomposition of a single reactant is first-order. Order, however, is derived from the rate law and can be whole numbers or fractions. An example is a reaction rate expressed as rate = k[A]^2[B]^1, indicating a 3rd order reaction overall.

Derive the integrated rate law for a first order reaction and explain how to use it to determine the rate constant.

For a first-order reaction, starting from \( \frac{d[R]}{dt} = -k[R] \), integrating gives the equation: \( \ln [R] = -kt + \ln [R]_0 \). To determine k, rearrange to obtain \( k = -\frac{\ln [R] - \ln [R]_0}{t} \). By measuring the concentration at two time points, k can be evaluated.

Explain the Arrhenius equation and its significance in chemical kinetics. Use it to calculate activation energy from given rate constants at two temperatures.

The Arrhenius equation \( k = Ae^{-Ea/RT} \) relates temperature to reaction rate constants. With two rate constants at different temperatures, the activation energy can be calculated using: \( \ln \left( \frac{k_2}{k_1} \right) = -\frac{E_a}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right) \). This demonstrates how temperature changes affect rate constants and reaction speed.

Describe collision theory as it relates to chemical kinetics. Discuss both the significance of activation energy and how changes in conditions can increase reaction rates.

Collision theory posits that for a reaction to occur, particles must collide with sufficient energy and proper orientation. Activation energy is the minimum energy needed for a reaction. Increasing temperature raises the average kinetic energy, leading to more frequent effective collisions. For example, increasing temperature can expedite a reaction between hydrogen and oxygen.

How can the rate of a chemical reaction be represented graphically? Provide a description of what a concentration vs time graph would indicate for zero and first order reactions.

A zero-order reaction graph shows a linear decrease in concentration over time, while a first-order reaction graph shows an exponential decay. For zero-order, the slope is -k, indicating constant reaction rate until reactant is exhausted. For first-order, the graph is logarithmic in appearance, with a slope of -k when plotted as ln[Reactant] against time.

Propose an experiment to determine the order of a reaction with respect to one reactant using initial rates method. Describe the expected observations.

Use varying concentrations of one reactant while keeping the other constant. Measure the initial rate of reaction for each concentration. Plot [Reactant] vs. Initial Rate; the graph's shape will indicate the order: linear for 1st order, parabolic for 2nd order, or flat for zero order. Analyze data to derive the order mathematically.

Evaluate the impact of a catalyst on a chemical reaction with respect to activation energy and reaction rate.

A catalyst provides an alternative pathway with a lower activation energy for the reaction, thus increasing the rate without undergoing permanent change itself. This results in a faster reaction and is essential for many industrial processes.

Chemical Kinetics - Challenge Worksheet

The final worksheet presents challenging long-answer questions that test your depth of understanding and exam-readiness for Chemical Kinetics in Class 12.

Challenge

Questions

Discuss the factors affecting the rate of food spoilage in terms of chemical kinetics. In your explanation, consider concentration, temperature, and catalysts in relation to reaction rates.

Analyze how each factor influences the kinetics of spoilage reactions, providing specific examples pertaining to food chemistry.

Evaluate the significance of collision theory in determining the rate of chemical reactions. How does molecular orientation affect reaction rates?

Contrast scenarios where collision theory applies and fails and discuss the implications for practical chemistry.

Analyze the rate law for the decomposition of hydrogen peroxide in terms of order of reaction. How does this compare with other common reactions like the one involving nitric oxide?

Provide a detailed comparison of reaction rates and orders found experimentally, elucidating any discrepancies with theoretical predictions.

Critically assess the role of temperature in influencing the rate constant of a reaction. Use the Arrhenius equation to illustrate your points.

Discuss how different temperatures can lead to varying activation energies and their effects, including graph them appropriately.

Predict the effects of a catalyst on a first-order reaction and derive the rate equation. What are the potential drawbacks of using catalysts in industrial applications?

Describe how catalysts lower activation energy, offering mechanical insight into reaction pathways.

Design an experiment to investigate the factors affecting the rate of the reaction between hydrochloric acid and sodium thiosulphate. What variables would you control?

Outline the methodology and include hypothetical data analysis along with the interpretation of results.

Evaluate how varying the concentration of reactants influences the rate of a second-order reaction and predict its integrated rate law.

Calculate hypothetical scenarios with different initial concentrations and their corresponding rates.

Given the following integrated rate equations, deduce their consequence on half-lives: Rate = k[A]², Rate = k[A]. Discuss how the half-life varies with concentration.

Provide mathematical derivations of half-life expressions for both zero and first-order reactions and evaluate their implications.

Consider the reaction 2A + B → products and its integrated form is given as: ln[A] = -kt + ln[A]₀. How does this indicate that reaction order affects its half-life?

Interpret the implications of the integrated form and its practical consequences in a structured manner.

Discuss real-world applications of kinetics in the automotive industry, particularly regarding fuel combustion rates. Which factors play a pivotal role, and how could they be quantified?

Illustrate your response through the formulation of kinetic models and explore experimental protocols to study combustion reactions.

Chemical Kinetics Formula Sheet

Use this Class 12 Chemistry Chemical Kinetics Formula Sheet for quick revision before school exams and CBSE exams. It brings together the important formulas, key concepts, and worked examples in one place so students can revise faster and download a printable PDF for offline study.

Important Formulas

Rate of reaction: r = -Δ[A]/Δt

r is the rate of reaction, Δ[A] is the change in concentration of reactant A, and Δt is the change in time. This formula defines the rate of disappearance of reactants as a function of time.

Rate constant (k): Rate = k[A]^x[B]^y

k is the rate constant, [A] and [B] are the molar concentrations of reactants A and B, while x and y are the reaction orders. This equation expresses how the reaction rate depends on reactant concentrations.

First-order reaction: ln[A] = -kt + ln[A]₀

In a first-order reaction, [A] is the concentration at time t, k is the rate constant, and [A]₀ is the initial concentration. This equation allows calculation of concentration at any time.

Zero-order reaction: [A] = [A]₀ - kt

For zero-order reactions, the concentration of A decreases linearly with time. [A]₀ is the initial concentration, and k is the rate constant.

Half-life for first-order reaction: t₁/₂ = 0.693/k

t₁/₂ represents the time required for half of the reactant to decompose in a first-order reaction. It is independent of initial concentration.

Arrhenius equation: k = Ae^(-Ea/RT)

k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin. This equation shows how temperature affects the rate constant.

Collision theory: Rate = Z * e^(-Ea/RT)

Z is the collision frequency of reactants. This equation models the rate of reactions based on molecular collisions and energy factors.

Order of reaction: n = x + y

n represents the overall order of the reaction derived from the rate law equation. It is the sum of the powers of concentrations of reactants.

Rate law: Rate = k[A]^x[B]^y

This formula relates the concentration of reactants to the rate of the reaction. x and y are the orders with respect to each reactant, determined experimentally.

Rate of formation of products: Rate = (1/c) * -Δ[Reactants]/Δt

For reactions producing products, where c is the stoichiometric coefficient for the reactants. This modifies the rate expression based on product formation.

Worked Examples

r = -Δ[A]/Δt

This represents the average rate of disappearance of reactant A per unit time.

ln(k₁/k₂) = -Ea/R(1/T₂ - 1/T₁)

This derives the relationship between the rate constants at two different temperatures, yielding the activation energy, Ea.

Rate = k[A][B]

For a second-order reaction involving two reactants, this defines the rate as proportional to the product of their concentrations.

k = 2.303/t₁/₂ * log([A]₀/[A])

This equation allows calculation of the rate constant k from the integrated form for a first-order reaction.

Rate = -1/a * Δ[A]/Δt

Where a is the stoichiometric coefficient of A, this adjusts the rate expression according to the coefficients in the balanced chemical equation.

k = [A]^n * [B]^m / rate

This reformulation derives k from concentrations and rate, showcasing its dependency on reactant concentrations.

t₁/₂ = 0.693/k

For first order reactions, half-life is a standardized measure to determine the time required for half of the reactant to be consumed.

Collision rate = Z = 𝑛 * v * (π * d²)

Describes molecular collision frequency where n is the concentration, v is velocity, and d is the diameter of the molecules.

Chance of effective collision = e^(-Ea/RT)

This describes the fraction of collisions that occur with sufficient energy to overcome the activation barrier.

Rate = k * (concentration of reactant)^order

Defines the collation between the rate of a reaction and concentration raised to the power of its order.

Explore More Chemical Kinetics Resources

Explore more chapter resources to strengthen your understanding and prepare for exams.

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Chemical Kinetics Frequently Asked Questions

Explore the concepts of Chemical Kinetics, including rates of reaction, factors affecting these rates, and practical applications in real-world chemistry.

QWhat is chemical kinetics?

Chemical kinetics is the study of the rates of chemical reactions and the factors affecting these rates. It provides insights into how quickly reactions occur and what influences their speed, enabling better control over chemical processes.

QHow do we measure the rate of a chemical reaction?

The rate of a chemical reaction can be measured by observing the change in concentration of reactants or products over time. It can be expressed as the rate of decrease in concentration of reactants or the rate of increase in concentration of products.

QWhat is the difference between average and instantaneous rate of reaction?

The average rate of reaction is calculated over a specific time interval, reflecting the overall change in concentration. In contrast, the instantaneous rate is the reaction rate at a specific moment, often determined using calculus by finding the slope of the tangent at a given point on the concentration-time curve.

QWhat determines the speed of a reaction?

The speed of a reaction is influenced by factors such as the concentrations of reactants, temperature, presence of a catalyst, and the physical state of the reactants. Higher concentrations and temperatures generally increase reaction rates.

QWhat is a rate law?

A rate law is an equation that relates the rate of a reaction to the concentration of its reactants, expressed in the form Rate = k[A]^x[B]^y, where k is the rate constant and x and y are the reaction orders with respect to each reactant.

QWhat is the significance of the rate constant?

The rate constant, denoted by k, quantifies the speed of a reaction under specific conditions. It varies with temperature and is influenced by the presence of catalysts. A higher k value indicates a faster reaction.

QWhat do molecularity and order of a reaction refer to?

Molecularity refers to the number of reacting species in an elementary reaction, while the order of a reaction is the sum of the powers of the concentration terms in its rate law. Order can be zero, whole numbers, or even fractions, whereas molecularity is always a whole number.

QHow do catalysts affect reaction rates?

Catalysts increase the rate of a chemical reaction by lowering the activation energy required for the reaction to occur. They provide an alternative pathway for the reaction, thus increasing the number of effective collisions between reactant molecules.

QWhat is collision theory?

Collision theory posits that for a reaction to occur, reacting particles must collide with sufficient energy and proper orientation. The rate of reaction depends on the collision frequency and the fraction of effective collisions.

QWhat are integrated rate equations?

Integrated rate equations relate the concentrations of reactants or products over time in a specific manner depending on the order of the reaction. They provide a mathematical way to calculate concentration at any time during the reaction.

QWhat is a zero-order reaction?

A zero-order reaction is one where the rate of reaction is constant and independent of the concentration of the reactants. The rate remains the same regardless of how much reactant is present, often occurring in enzyme-catalyzed or surface reactions.

QWhat is a first-order reaction?

A first-order reaction is one where the rate of reaction is directly proportional to the concentration of one reactant. If the concentration of the reactant doubles, the reaction rate also doubles.

QHow does temperature affect reaction rates?

Increasing temperature generally increases the rate of reaction. It provides molecules with more kinetic energy, resulting in more frequent and effective collisions. The relationship between temperature and rate constants can be described by the Arrhenius equation.

QWhat is the Arrhenius equation?

The Arrhenius equation describes the temperature dependence of reaction rates. It states that the rate constant k equals the pre-exponential factor A multiplied by the exponential of the negative activation energy E_a divided by the product of the gas constant R and temperature T.

QHow can we graphically represent first-order reactions?

For first-order reactions, a plot of ln [R] versus time yields a straight line with a slope of -k, where [R] is the concentration of the reactant. This linear relationship can be used to determine the rate constant k.

QWhat is half-life in the context of chemical kinetics?

Half-life is the time required for the concentration of a reactant to decrease to half of its initial concentration. It is particularly important in first-order reactions, where the half-life is constant and independent of the initial concentration.

QWhat does it mean if a reaction is pseudo-first-order?

A reaction is termed pseudo-first-order when it appears to follow first-order kinetics, but in reality, it's a higher-order reaction. This occurs when one reactant is in large excess, rendering its concentration relatively constant throughout the reaction.

QHow is the rate of reaction affected when one reactant concentration is tripled?

If a reaction is second-order with respect to a reactant, tripling its concentration will increase the rate by a factor of nine (3^2). If it's first-order, the rate will simply triple.

QHow can we experimentally determine the order of a reaction?

The order of a reaction can be experimentally determined by measuring the initial rate of reaction while varying the concentration of the reactants. Analyzing these rates against their respective concentrations allows for the derivation of the rate law and its order.

QWhat is the role of pressure in gas-phase reactions?

In gas-phase reactions, pressure is related to concentration. Increased pressure effectively increases the number of collisions among gas molecules, potentially increasing the reaction rate. Rate laws for gas-phase reactions can also be expressed in terms of partial pressures.

QWhat factors can affect the rate of reaction in a laboratory setting?

In a laboratory setting, factors affecting reaction rates include temperature, concentration of reactants, surface area, presence and type of catalysts, and pressure (in the case of gaseous reactions).

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1/20

What is the rate of a reaction?

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The rate of a reaction is the change in concentration of a reactant or product per unit time, expressed in mol L⁻¹ s⁻¹.

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2/20

How is the average rate of reaction defined?

2/20

Average rate is defined as the change in concentration of reactants or products over a specific time period. Formulated as Rate = -Δ[R]/Δt or Rate = Δ[P]/Δt.

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3/20

What is the difference between kinetics and thermodynamics?

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3/20

Kinetics studies the rate of chemical reactions, while thermodynamics focuses on the feasibility and energy aspects of reactions.

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4/20

What does collision theory state?

4/20

Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy and proper orientation.

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What factors affect the rate of a chemical reaction?

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Factors include concentration, temperature, pressure, and the presence of a catalyst.

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What is the instantaneous rate of reaction?

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The instantaneous rate is the rate of reaction at a specific time, determined by the slope of the concentration vs. time graph.

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What are the units of a reaction rate?

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Units are typically mol L⁻¹ s⁻¹ for solutions or atm s⁻¹ for gaseous reactions.

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What is a rate law?

8/20

A rate law expresses the rate of a reaction as a function of the concentrations of the reactants, typically in the form Rate = k[A]^m[B]^n.

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What is the order of a reaction?

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The order of a reaction is the sum of the powers of the concentration terms in the rate law, indicating how the rate depends on reactant concentrations.

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What characterizes a zero-order reaction?

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In a zero-order reaction, the rate is constant and does not depend on the concentration of reactants.

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How do first-order reactions behave?

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The rate of a first-order reaction is directly proportional to the concentration of one reactant. The rate decreases as the concentration decreases.

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What defines a second-order reaction?

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A second-order reaction rate is proportional to the square of the concentration of one reactant or the product of two different reactants' concentrations.

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What is the role of a catalyst?

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A catalyst increases the rate of a reaction by lowering the activation energy without being consumed in the process.

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How does temperature affect reaction rate?

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Increasing temperature generally increases the reaction rate, as it enhances particle movement and collision frequency.

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How does pressure influence reaction rates in gases?

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Increasing pressure in gaseous reactions typically increases the reaction rate by reducing the volume and increasing concentration.

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Give an example of a fast reaction.

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The precipitation of silver chloride is an example of a fast reaction that occurs immediately upon mixing reactants.

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What is an example of a slow reaction?

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The rusting of iron is an example of a slow reaction that takes place over an extended period.

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What is activation energy?

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Activation energy is the minimum energy required for reactants to collide effectively and initiate a chemical reaction.

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What is chemical equilibrium?

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Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in a constant concentration of reactants and products.

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How does concentration affect reaction rates?

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Higher concentration of reactants generally leads to a higher reaction rate due to increased collision frequency.

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