Podcast
Questions and Answers
What is one primary reason for studying the rates of reaction in chemical kinetics?
What is one primary reason for studying the rates of reaction in chemical kinetics?
- To determine the final products of a reaction
- To identify reactants in a reaction
- To better understand reaction mechanisms (correct)
- To calculate the equilibrium constant
How does increasing concentration affect the rate of a chemical reaction?
How does increasing concentration affect the rate of a chemical reaction?
- It changes the activation energy required for the reaction
- It has no effect on the reaction rate
- It decreases the vibrational energy of the molecules
- It increases the frequency of molecular collisions (correct)
What is the role of catalysts in chemical reactions?
What is the role of catalysts in chemical reactions?
- To initiate a reaction only at high temperatures
- To increase the rate of reaction by providing an alternative pathway (correct)
- To completely change the products of a reaction
- To slow down the reaction rate for better control
What does the collision theory state regarding the rate of reaction?
What does the collision theory state regarding the rate of reaction?
Which of the following statements about temperature's effect on reaction rates is true?
Which of the following statements about temperature's effect on reaction rates is true?
What happens to the reaction rate when the concentration of reactant [A] is doubled for a first-order reaction?
What happens to the reaction rate when the concentration of reactant [A] is doubled for a first-order reaction?
For a second-order reaction, what is the relationship between the concentration of reactant [A] and the rate constant k when [A] is tripled?
For a second-order reaction, what is the relationship between the concentration of reactant [A] and the rate constant k when [A] is tripled?
What is the overall reaction order in the reaction: F₂ + 2ClO₂ → 2ClO₂F if both reactants are first-order?
What is the overall reaction order in the reaction: F₂ + 2ClO₂ → 2ClO₂F if both reactants are first-order?
Which of the following statements about the units of the rate constant k is correct for a second-order reaction?
Which of the following statements about the units of the rate constant k is correct for a second-order reaction?
What does the rate law express in a chemical reaction?
What does the rate law express in a chemical reaction?
What effect does a catalyst have on the activation energy of a reaction?
What effect does a catalyst have on the activation energy of a reaction?
Which of the following substances can act as a catalyst?
Which of the following substances can act as a catalyst?
How does an increase in temperature affect the fraction of molecules that can react?
How does an increase in temperature affect the fraction of molecules that can react?
What does the symbol 'R' represent in the equation for the rate constant?
What does the symbol 'R' represent in the equation for the rate constant?
What happens to the position of equilibrium when a catalyst is introduced in a reaction?
What happens to the position of equilibrium when a catalyst is introduced in a reaction?
In the context of chemical kinetics, what does the term 'Ea' stand for?
In the context of chemical kinetics, what does the term 'Ea' stand for?
At which temperature does the fraction of molecules capable of reacting, specifically with an activation energy of 50,000 J/mol, significantly increase?
At which temperature does the fraction of molecules capable of reacting, specifically with an activation energy of 50,000 J/mol, significantly increase?
What is the primary factor that affects the rate constant 'k' in the equation k = A e^{-Ea/RT}?
What is the primary factor that affects the rate constant 'k' in the equation k = A e^{-Ea/RT}?
What does the Maxwell-Boltzmann distribution indicate about gas molecules?
What does the Maxwell-Boltzmann distribution indicate about gas molecules?
How does increasing the temperature affect the number of particles capable of reacting?
How does increasing the temperature affect the number of particles capable of reacting?
What does the variable 'k' in the Arrhenius equation represent?
What does the variable 'k' in the Arrhenius equation represent?
Which statement about activation energy (Ea) is correct?
Which statement about activation energy (Ea) is correct?
What can be deduced from varying experiments regarding the rate constant 'k'?
What can be deduced from varying experiments regarding the rate constant 'k'?
In the Arrhenius equation, what does the letter 'R' stand for?
In the Arrhenius equation, what does the letter 'R' stand for?
What effect does temperature have on the average energy of particles in a system?
What effect does temperature have on the average energy of particles in a system?
What does the term 'shelf life' refer to in the context of the Arrhenius equation?
What does the term 'shelf life' refer to in the context of the Arrhenius equation?
How does the Arrhenius equation help in understanding chemical reactions?
How does the Arrhenius equation help in understanding chemical reactions?
What is the primary consequence of increasing the temperature in a reaction system?
What is the primary consequence of increasing the temperature in a reaction system?
What predominantly influences the rate of collision for a gas?
What predominantly influences the rate of collision for a gas?
How does surface area affect the rate of a chemical reaction?
How does surface area affect the rate of a chemical reaction?
Why is correct molecular orientation important in chemical reactions?
Why is correct molecular orientation important in chemical reactions?
How does temperature affect molecular speed?
How does temperature affect molecular speed?
What is the average energy of molecules at 20°C approximately?
What is the average energy of molecules at 20°C approximately?
What relationship does the activation energy have with the transition state?
What relationship does the activation energy have with the transition state?
What is the average reaction success rate for complex reactions?
What is the average reaction success rate for complex reactions?
Which of the following factors do NOT influence the collision rate?
Which of the following factors do NOT influence the collision rate?
What is true about the energy barrier for most reactions?
What is true about the energy barrier for most reactions?
In the reaction of Mg(s) with H+, how does surface area impact the reaction?
In the reaction of Mg(s) with H+, how does surface area impact the reaction?
What is the order of the reaction with respect to reactant A when the rate equation is rate = k[A]?
What is the order of the reaction with respect to reactant A when the rate equation is rate = k[A]?
In an SN1 reaction involving tert-butyl chloride and hydroxyl anion, what is the overall effect of increasing the concentration of OH- on the reaction rate?
In an SN1 reaction involving tert-butyl chloride and hydroxyl anion, what is the overall effect of increasing the concentration of OH- on the reaction rate?
Which statement accurately describes the overall order of reaction when both reactants A and B are included in the rate equation rate = k[A][B]?
Which statement accurately describes the overall order of reaction when both reactants A and B are included in the rate equation rate = k[A][B]?
For the SN2 reaction involving chloromethane and hydroxyl anion, what can be inferred about the order with respect to both reactants?
For the SN2 reaction involving chloromethane and hydroxyl anion, what can be inferred about the order with respect to both reactants?
In the reaction rate = k[B]^2, what is the order of reaction with respect to B?
In the reaction rate = k[B]^2, what is the order of reaction with respect to B?
What is the order of the SN1 reaction with respect to (CH3)3CBr?
What is the order of the SN1 reaction with respect to (CH3)3CBr?
When the slow step of a reaction mechanism is first, which statement is true regarding the order of the reaction with respect to each reactant involved?
When the slow step of a reaction mechanism is first, which statement is true regarding the order of the reaction with respect to each reactant involved?
What can be concluded from the rate equation rate = k[B]^2 regarding the behavior of reactant B?
What can be concluded from the rate equation rate = k[B]^2 regarding the behavior of reactant B?
What is the primary purpose of studying the rates of reaction in chemical kinetics?
What is the primary purpose of studying the rates of reaction in chemical kinetics?
Which of the following factors is NOT directly related to the collision rate in chemical reactions?
Which of the following factors is NOT directly related to the collision rate in chemical reactions?
In the context of chemical kinetics, what does an increase in concentration imply about reaction order?
In the context of chemical kinetics, what does an increase in concentration imply about reaction order?
Which of the following best describes the relationship between temperature and the rate of reaction according to collision theory?
Which of the following best describes the relationship between temperature and the rate of reaction according to collision theory?
How does the introduction of a catalyst function in a chemical reaction?
How does the introduction of a catalyst function in a chemical reaction?
How does the collision rate change in a gas when pressure is increased?
How does the collision rate change in a gas when pressure is increased?
What is the relationship between temperature and molecular speed as described by kinetic theory?
What is the relationship between temperature and molecular speed as described by kinetic theory?
What is the typical activation energy range for many chemical reactions?
What is the typical activation energy range for many chemical reactions?
In complex reactions, what is the likelihood of successful reactions occurring based on collisions?
In complex reactions, what is the likelihood of successful reactions occurring based on collisions?
Which factor is NOT considered to be directly affected by the activation energy in a reaction?
Which factor is NOT considered to be directly affected by the activation energy in a reaction?
What does the Maxwell-Boltzmann distribution illustrate in the context of gas reactions?
What does the Maxwell-Boltzmann distribution illustrate in the context of gas reactions?
At what temperature is the average energy of molecules approximately 4 kJ/mol?
At what temperature is the average energy of molecules approximately 4 kJ/mol?
How does the increase in surface area affect the rate of a reaction?
How does the increase in surface area affect the rate of a reaction?
What can be concluded when both A and B participate in the slow step of a reaction mechanism?
What can be concluded when both A and B participate in the slow step of a reaction mechanism?
When the slow step is not first in the mechanism, how is the rate expression affected?
When the slow step is not first in the mechanism, how is the rate expression affected?
What must be true for a reaction mechanism if the observed reaction order is first with respect to A and B?
What must be true for a reaction mechanism if the observed reaction order is first with respect to A and B?
How can one derive a new rate equation when a reactant involved in the slow step is not initially present?
How can one derive a new rate equation when a reactant involved in the slow step is not initially present?
Why is mechanism 1 ruled out in the provided scenario based on the slow step analysis?
Why is mechanism 1 ruled out in the provided scenario based on the slow step analysis?
What is the overall order of the reaction when the rate law is expressed as rate = k[A][B]?
What is the overall order of the reaction when the rate law is expressed as rate = k[A][B]?
In the rate equation rate = k[B]^2, how does the concentration of B affect the rate of reaction?
In the rate equation rate = k[B]^2, how does the concentration of B affect the rate of reaction?
What characteristic defines an SN1 reaction based on the given information?
What characteristic defines an SN1 reaction based on the given information?
How does doubling the concentration of [H+] influence the rate of a reaction if the rate quadruples?
How does doubling the concentration of [H+] influence the rate of a reaction if the rate quadruples?
In the SN2 reaction of chloromethane and a hydroxyl anion, which of the following statements about the rate law is accurate?
In the SN2 reaction of chloromethane and a hydroxyl anion, which of the following statements about the rate law is accurate?
Which statement correctly explains how reaction rates change when concentrations of reactants are increased for a second-order reaction?
Which statement correctly explains how reaction rates change when concentrations of reactants are increased for a second-order reaction?
In which scenario does increasing the concentration of a reactant NOT lead to an increased reaction rate?
In which scenario does increasing the concentration of a reactant NOT lead to an increased reaction rate?
Which of the following is true about the rate law derived from a unimolecular step in the reaction mechanism?
Which of the following is true about the rate law derived from a unimolecular step in the reaction mechanism?
What is the overall order of the reaction for F₂ + 2ClO₂ → 2ClO₂F based on the experimental data?
What is the overall order of the reaction for F₂ + 2ClO₂ → 2ClO₂F based on the experimental data?
How does the rate constant k relate to the units of reaction order in chemical kinetics?
How does the rate constant k relate to the units of reaction order in chemical kinetics?
What happens to the initial rate of reaction when the concentration of ClO₂ is quadrupled if the reaction order with respect to ClO₂ is 1?
What happens to the initial rate of reaction when the concentration of ClO₂ is quadrupled if the reaction order with respect to ClO₂ is 1?
In the rate law for the reaction aA + bB + cC → dD + eE, which term represents the overall reaction order?
In the rate law for the reaction aA + bB + cC → dD + eE, which term represents the overall reaction order?
What is the effect on the rate of reaction, when the concentration of reactant A in a first-order reaction is tripled?
What is the effect on the rate of reaction, when the concentration of reactant A in a first-order reaction is tripled?
If the rate of a second-order reaction is increased when the concentration of one reactant is doubled, what happens to the rate when both reactants are increased by a factor of two?
If the rate of a second-order reaction is increased when the concentration of one reactant is doubled, what happens to the rate when both reactants are increased by a factor of two?
What is a key requirement for the rate constant k in relation to the initial rate of reaction and concentration of reactants?
What is a key requirement for the rate constant k in relation to the initial rate of reaction and concentration of reactants?
If the initial rate of a reaction is expressed as rate = k[A][B], how will the rate change if the concentration of both A and B are halved?
If the initial rate of a reaction is expressed as rate = k[A][B], how will the rate change if the concentration of both A and B are halved?
What does the frequency factor (A) in the Arrhenius equation represent?
What does the frequency factor (A) in the Arrhenius equation represent?
How does a catalyst affect the activation energy (Ea) of a reaction?
How does a catalyst affect the activation energy (Ea) of a reaction?
Which of the following statements about molecularity is correct?
Which of the following statements about molecularity is correct?
In the context of chemical kinetics, what is the primary function of enzymes?
In the context of chemical kinetics, what is the primary function of enzymes?
What represents the fraction of molecules with sufficient energy to react in the Arrhenius equation?
What represents the fraction of molecules with sufficient energy to react in the Arrhenius equation?
Why is the term 'shelf life' relevant to the Arrhenius equation?
Why is the term 'shelf life' relevant to the Arrhenius equation?
Which of the following describes the impact of a 10°C increase in temperature on the reaction rate?
Which of the following describes the impact of a 10°C increase in temperature on the reaction rate?
In a multi-step reaction, which term best describes the rate of the overall process?
In a multi-step reaction, which term best describes the rate of the overall process?
What is the significance of the gas constant (R) in the Arrhenius equation?
What is the significance of the gas constant (R) in the Arrhenius equation?
Flashcards
Chemical Kinetics
Chemical Kinetics
The study of reaction rates and factors influencing them, providing insights into how reactions occur.
Reaction Mechanism
Reaction Mechanism
The pathway a reaction takes, involving the steps that lead from reactants to products.
Reaction Rate
Reaction Rate
The rate at which reactants are consumed or products are formed in a given time period.
Rate Constant (k)
Rate Constant (k)
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Activation Energy (Ea)
Activation Energy (Ea)
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Effect of Concentration on Reaction Rate
Effect of Concentration on Reaction Rate
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Effect of Temperature on Reaction Rate
Effect of Temperature on Reaction Rate
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Catalyst
Catalyst
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Collision Theory
Collision Theory
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Rate Law
Rate Law
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Order of Reaction
Order of Reaction
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First-Order Reaction
First-Order Reaction
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Second-Order Reaction
Second-Order Reaction
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Fraction of Reactive Molecules
Fraction of Reactive Molecules
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Maxwell-Boltzmann Distribution
Maxwell-Boltzmann Distribution
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Significant Temperature
Significant Temperature
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Arrhenius Equation
Arrhenius Equation
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Rate Equation (Rate Law)
Rate Equation (Rate Law)
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Multi-Step Reaction
Multi-Step Reaction
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Rate-Determining Step
Rate-Determining Step
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Zero-Order Reaction
Zero-Order Reaction
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Rate-Determining Reactant
Rate-Determining Reactant
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Complex Reaction
Complex Reaction
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SN1 Reaction
SN1 Reaction
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SN2 Reaction
SN2 Reaction
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Order of Reaction (with respect to a reactant)
Order of Reaction (with respect to a reactant)
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First-Order with Respect to a Reactant
First-Order with Respect to a Reactant
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Second-Order with Respect to a Reactant
Second-Order with Respect to a Reactant
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Zero-Order with Respect to a Reactant
Zero-Order with Respect to a Reactant
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Zero Order
Zero Order
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Activation Energy
Activation Energy
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Effect of Pressure on Reaction Rate
Effect of Pressure on Reaction Rate
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Effect of Molecular Orientation
Effect of Molecular Orientation
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Effect of Temperature on Molecular Speed
Effect of Temperature on Molecular Speed
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Energy Barrier
Energy Barrier
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Temperature and Activation Energy
Temperature and Activation Energy
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Molecularity
Molecularity
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Unimolecular Reaction
Unimolecular Reaction
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Overall Order of Reaction
Overall Order of Reaction
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Reaction order (with respect to a reactant)
Reaction order (with respect to a reactant)
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Overall reaction order
Overall reaction order
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Rate equation
Rate equation
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Study Notes
Chemical Kinetics: Rate & Order of Reaction
- The topic is chemical kinetics, specifically focusing on reaction rates and orders.
- The lecture is delivered by Dr. Stephen Childs, a Senior Lecturer in Pharmaceutical Chemistry at the University of Sunderland.
- Contact information for Dr. Childs is provided.
- Recommended reading material is Atkins' Physical Chemistry, Chapters 21.2 - 21.5 (9th Edition).
Why Study Reaction Rates?
- Understanding reaction mechanisms (e.g., SN1 and SN2).
- Optimizing reaction rates to improve yields and reduce byproducts.
- Minimizing drug degradation and improving shelf-life (e.g., pH-dependent hydrolysis of aspirin).
- Understanding what drives a reaction forward (e.g., H2 + 1/2 O2 → H2O; ΔH = -286 kJ/mol).
What Affects Reaction Rate?
- Physical state: Many relevant reactions occur in solution.
- Concentration: Molecules must collide to react; increased concentration leads to increased collision frequency.
- Temperature: Higher temperature increases collision frequency and vibrational energy of bonds.
- Catalysts: Catalysts provide alternative reaction mechanisms with lower activation energies.
Collision Theory
- Reaction rate depends on the frequency of collisions with sufficient energy to react.
- Factors influencing collision rate include:
- Concentration: Increased concentration = increased collision frequency, depending on the order of the reaction.
- Pressure (for gases): Increased pressure increases the reaction rate due to increased collisions.
- Surface area: Larger surface area leads to higher collision rates.
- Molecular orientation: Correct orientation is essential for successful collisions
- Temperature: Increased temperature leads to greater molecular speeds and more frequent high-energy collisions.
Effect of Surface Area
- Collision rate depends on the available surface area.
- Example: Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g).
Effect of Molecular Orientation
- Not all collisions result in a reaction.
- Correct molecular orientation is important, particularly in complex reactions.
- Example: HCl and ethene (electrophilic addition) - orientational collisions only occur in ~1/105
Effect of Molecular Speed
- Collision rate depends on molecular speed.
- Temperature affects molecular speed, as per kinetic theory of gases.
- Formula: Vrms = √(3RT/M) (Vrms = root mean square speed, R is ideal gas constant, T temperature, M mass).
Activation Energy
- Energy barrier associated with the transition state.
- Molecular shape distortion during the transition state.
- Energy barriers (~50-100 kJ) are necessary for reactions, despite the average energy at temperatures (~4 kJ approx).
- Only a small fraction of molecules (about 1 in 109) have enough energy to overcome the barrier.
Maxwell-Boltzmann Distribution
- For gases, the number of molecules with sufficient energy to react can be represented by a curve.
- The area under the curve at higher energies corresponds to the reactant molecules with sufficient energy to undergo reaction.
Effect of Temperature
- Increasing temperature significantly increases the number of particles exceeding the activation energy.
Arrhenius Equation
- Increasing temperature increases the rate constant (k).
- Relating k to temperature, the Arrhenius equation is: k = Ae-Ea/RT.
- Variables include:
- k: Rate constant
- A: Frequency factor (pre-exponential factor)
- Ea: Activation energy
- R: Gas constant (8.3145 J mol-1 deg-1) -T: Absolute temperature (in Kelvin).
Effect of Temperature II
- Assuming a certain activation energy and temperatures, the fraction of molecules with sufficient energy to react increases significantly with just a slight increase in temperature.
Catalysts
- Catalysts increase reaction rates without being consumed.
- Provide a lower activation energy pathway.
- Example: Acid-catalyzed hydrolysis of esters and chlorine radicals catalyzing ozone decomposition.
Catalysts II
- Catalysts do not alter the equilibrium position of a reaction.
- Do not change the overall Gibbs free energy change (ΔG).
- Enzymes, as biological catalysts, are proteins
Rate of Reaction
- Measuring reactant concentration changes over time.
- Change in reactant concentration
- Change in product concentration
Measuring Rates of Reaction
- The provided graph illustrates the progression of a reaction over time using the concentration of reactant A ([A]) as the dependent variable.
Chemical Reactions II
- Most reactions are multi-step processes.
- Example: A multi-step NOx reaction.
- Molecularity: Number of molecules involved in an elementary step.
- Unimolecular; bimolecular; termolecular: Based upon the number of molecules.
Rate of Reaction II
- What happens when you increase the reactant concentration ([A])?
- Rate independent of [A]: The rate is not affected by changes in concentration [A] if the rate law is independent of [A].
- First-order reactions: Doubling [A] doubles the rate
- Second-order reactions: Doubling [A] quadruples the rate.
Reaction Order (i)
- Rate Multiplication, Reaction Order, Rate constant (k) units in table format.
- The rate law is the sum of reactant orders.
- Example reaction:aA+bB+cC−→dD+eE, rate = k[A]x [B]y[C]zwhere x, y and z are the orders of A, B, and C respectively.
Reaction Order II
- Graphs visually depicting the change in reactant concentration over time for zero, first, and second-order reactions.
Reaction Order III
- Example (F2+2ClO2→2ClO2F) demonstrating determining reaction orders from experimental data.
- Determining rate laws for reactions based on experimental data, and calculate the overall order of the reaction.
Reaction Order IV
- Example (BrO3- + 5Br + 6H+ —> 3Br2 + 3H2O), illustrating determining reaction order from data.
- Determining rate laws for reactions based on experimental data, and calculate the overall order of the reaction.
Rate Law Examples
- The reaction rate between A + B.
- Rates as a function of reactant concentration.
- Examples of different reaction orders (first, second, zero, etc.).
Reaction Mechanisms I
- SN1 reaction (tert-butyl chloride and hydroxyl anion).
- Determining reaction rate orders to deduce the reaction mechanism.
- Unimolecular mechanism (step 1 - rate-determining).
- Fast reactions that don’t affect overall reaction rates (step 2).
Reaction Mechanisms II
- SN2 reaction (chloromethane and hydroxyl anion).
- Bimolecular reaction.
Determining Mechanisms I
- Determining the correct reaction mechanism by using the reaction order, and which mechanism fits the reaction.
Determining Mechanisms II
- Analyzing reaction mechanisms where the rate-determining step is not the first step.
- Rate and equilibrium constants that can be used to determine a rate.
- Obtaining an overall rate from equilibrium constant and initial rate law.
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