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Questions and Answers
What can be inferred if a reaction rate does not depend on the concentration of reactant C?
What can be inferred if a reaction rate does not depend on the concentration of reactant C?
Reaction rates provide insight into how fast products are produced but do not teach us anything about the reaction mechanism.
Reaction rates provide insight into how fast products are produced but do not teach us anything about the reaction mechanism.
False
What analogy is used to explain the independence of reaction rates from reactants?
What analogy is used to explain the independence of reaction rates from reactants?
A cookie factory.
Knowledge of reaction kinetics helps us understand what happens inside the _______.
Knowledge of reaction kinetics helps us understand what happens inside the _______.
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Match the following concepts related to reaction rates.
Match the following concepts related to reaction rates.
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What is the primary factor that affects the speed of chemical reactions according to chemical kinetics?
What is the primary factor that affects the speed of chemical reactions according to chemical kinetics?
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Heating a reaction generally decreases the speed of the reaction.
Heating a reaction generally decreases the speed of the reaction.
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What happens to ant speed when the temperature increases by 10°C?
What happens to ant speed when the temperature increases by 10°C?
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The rate law is expressed as Rate = k[A]^[m][B]^[n], where k is the rate constant, and __________ represents the order of the reaction.
The rate law is expressed as Rate = k[A]^[m][B]^[n], where k is the rate constant, and __________ represents the order of the reaction.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What is the primary unit used to quantify the change in concentration in reaction rates?
What is the primary unit used to quantify the change in concentration in reaction rates?
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The rate of disappearance of a reactant is always considered a positive value.
The rate of disappearance of a reactant is always considered a positive value.
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What happens to the average reaction rate as the time interval approaches zero?
What happens to the average reaction rate as the time interval approaches zero?
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The formula for average reaction rate is given by ___________.
The formula for average reaction rate is given by ___________.
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Match the reaction components with their descriptions:
Match the reaction components with their descriptions:
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Which of the following statements about average and instantaneous reaction rates is true?
Which of the following statements about average and instantaneous reaction rates is true?
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Brackets around concentration symbols indicate molarity.
Brackets around concentration symbols indicate molarity.
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In the context of reaction rates, what does 'M' stand for?
In the context of reaction rates, what does 'M' stand for?
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What describes the slope of the line in the context of second-order kinetics?
What describes the slope of the line in the context of second-order kinetics?
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For zero-order reactions, the rate of reaction depends on the concentration of reactant A.
For zero-order reactions, the rate of reaction depends on the concentration of reactant A.
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What is the general expression for the rate of a zero-order reaction?
What is the general expression for the rate of a zero-order reaction?
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In order to analyze the reaction kinetics, one can plot __________ versus time.
In order to analyze the reaction kinetics, one can plot __________ versus time.
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What happens when [A] decreases in zero-order reactions?
What happens when [A] decreases in zero-order reactions?
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The equation d[A]/dt = -k[A] represents first-order kinetics.
The equation d[A]/dt = -k[A] represents first-order kinetics.
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For a second-order reaction, the integrated rate law shows a relationship between __________ and time.
For a second-order reaction, the integrated rate law shows a relationship between __________ and time.
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What is the rate equation derived from the given experiments?
What is the rate equation derived from the given experiments?
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The initial rate of Reaction 3 is greater than the initial rate of Reaction 1.
The initial rate of Reaction 3 is greater than the initial rate of Reaction 1.
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What is the significance of comparing experimental rates in determining the order of a reaction?
What is the significance of comparing experimental rates in determining the order of a reaction?
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The reaction rate equation commonly follows the form Rate = k[A]^x[B]^y, where x and y denote the __________ of the reactants.
The reaction rate equation commonly follows the form Rate = k[A]^x[B]^y, where x and y denote the __________ of the reactants.
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Match the experimental conditions with their corresponding initial rates:
Match the experimental conditions with their corresponding initial rates:
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What effect does doubling the concentration of A have on the reaction rate based on the experiments?
What effect does doubling the concentration of A have on the reaction rate based on the experiments?
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The order of the reaction with respect to B can be confirmed by comparing the initial rates from Experiment 1 and Experiment 2.
The order of the reaction with respect to B can be confirmed by comparing the initial rates from Experiment 1 and Experiment 2.
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What does the rate law k[A]^x[B]^y represent in a chemical reaction?
What does the rate law k[A]^x[B]^y represent in a chemical reaction?
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What does the reaction half-life t1/2 represent?
What does the reaction half-life t1/2 represent?
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The half-life of a zero order reaction is proportional to the initial concentration of reactant.
The half-life of a zero order reaction is proportional to the initial concentration of reactant.
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What is the equation for the half-life of a first order reaction?
What is the equation for the half-life of a first order reaction?
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In a second order reaction, the half-life is __________ proportional to the initial concentration.
In a second order reaction, the half-life is __________ proportional to the initial concentration.
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Match the following reaction orders with their traits:
Match the following reaction orders with their traits:
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Which term best describes the relationship between the reaction rate and the rate constant k?
Which term best describes the relationship between the reaction rate and the rate constant k?
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The half-lives of second order reactions increase as the initial concentration of reactants decreases.
The half-lives of second order reactions increase as the initial concentration of reactants decreases.
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What does a bigger rate constant (k) indicate about a chemical reaction?
What does a bigger rate constant (k) indicate about a chemical reaction?
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The half-life for a zero order reaction can be calculated as t1/2 = ________.
The half-life for a zero order reaction can be calculated as t1/2 = ________.
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Which statement is true regarding the half-lives across different orders of reactions?
Which statement is true regarding the half-lives across different orders of reactions?
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Study Notes
Lecture Announcements
-
Today's Topics: Brown Chapter 14, Chemical Kinetics I
- 14.1 Factors Affecting Reaction Rates
- 14.2 Reaction Rates
- 14.3 Concentration and Rate Laws
- 14.4 Change of Concentration with Time
- Problem Set 9: Due before Exercise #10 tomorrow, upload to Moodle.
- Problem Set 10: Posted on Moodle, due before Exercise #11 next week.
- Study Center: Wednesdays 6:00 PM - 8:00 PM in ETA F5
- Office Hours: Professor Norris and Brisby, Thursdays 5:00 PM - 6:00 PM in LEE P 210
Lecture 11
-
Next Week's Topics: Brown Chapter 14, Chemical Kinetics II
- 14.5 Temperature and Rate
- 14.6 Reaction Mechanisms
- 14.7 Catalysis
Red Thread
- Topics Order: Properties, Kinetics, Catalysis, Equilibrium, Acid-Base, Batteries, Christmas
Review
-
Lecture 9 Topics: Solutions
- Thermodynamics of solutions (ΔGsoln, ΔHsoln, ΔSsoln)
- Solubility (miscible, immiscible, saturated)
- Solubility factors (polarity, temperature, pressure)
- Henry's Law (solubility of gases in liquids)
- Expressions for concentration
- Colligative Properties:
- Boiling-point elevation
- Vapor-pressure lowering
- Ideal solutions (Raoult's law)
- Freezing-point depression
- Osmosis and osmotic pressure
Antifreeze Proteins (AFPs)
- Description: Polypeptides in animals, plants, fungi, and bacteria that allow survival in sub-freezing temperatures.
- Mechanism: Unlike antifreeze chemicals, AFPs act via a non-colligative manner, minimizing their effect on osmotic pressure while maintaining antifreeze properties at much lower concentrations.
- Function: Selective affinity for specific crystalline ice forms, blocking ice nucleation.
- Process: Uses kinetics instead of thermodynamics.
Chemical Kinetics
- Importance: Thermodynamics tells us if a reaction or process is possible, but kinetics tells us how fast it happens. Important for reaction speed.
- Key Parameters: Concentration, time, temperature
- Reaction Mechanism: Kinetics helps understand the steps involved, leading to reaction optimization.
Reaction Rate
- Definition: Rate is the rate of change in concentration of reactants or products over time.
- Units: Typically expressed as M/s (moles per liter per second).
Average vs. Instantaneous Reaction Rates
- Average Rate: Change in concentration over a time interval.
- Instantaneous Rate: Change in concentration at a particular moment in time.
- Difference: Generally, the instantaneous rate differs from the average rate across a larger interval of time.
Plot Concentrations versus Time
- Instantaneous Rate vs. Time: Describes how fast a reaction proceeds at individual points within the reaction process.
- Correlation to Reactants: As one reactant is consumed, the rate of the reaction will typically decrease.
But Curve Shape Depends on Specific Reaction
- Average Rate vs. Instantaneous Rate: Rates can be constant or vary widely.
- Relationship to Reaction: Plots can indicate if the rates are constant or whether the process is dependent on the reactant being consumed.
What Does This Mean?
- Reaction Independence: Reaction rates can be independent of initial reactant concentrations.
- Analogy: Real-world example of a "black box" (a reaction) or system where the rate of production is independent of initial resources.
What Do Reaction Rates Tell Us?
- Mechanism Insight: Kinetics allows for insight into the reaction mechanism.
- Optimization: Knowledge of how reactions work allows optimization.
Our Terminology
- Rate: Instantaneous rate at time, t
- Initial Rate: Instantaneous rate at t = 0
- Stoichiometric Coefficients: Used in defining the reaction rate in a more precise manner. This convention is necessary due to these coefficients.
- Examples: -2 O3(g) → 3 O2(g) Rate = (1/2) d[O3]/dt = (1/3) d[O2]/dt
Rate Laws
- Definition: Expressions that relate reaction rates to concentrations for the overall reaction.
- General Form: Rate = k[A]m[B]n -k → Rate constant -m, n → Reaction orders
Rate Laws - Additional Notes
- More Reactants: The rate law will contain terms for each reactant.
- Overall Reaction Order: The sum of the exponents in a rate law.
- Units of k: Depend on the overall reaction order.
Determining Rate Laws
- Experimental Data: Used to determine the rate law.
- Data Treatment: Compare reactions in which initial concentrations of one reactant are held constant while the other changes to help determine the overall reaction order.
Using Rate Laws
- Concentration Change: Allows determination of how concentrations change over time.
- Cases: Three possible cases for understanding first order reactions with respect to reactant concentrations.
First-Order Reactions
- Differential Equation: d[A]/dt = -k[A]
- Integrated Equation: ln[A]t = -kt + ln[A]0
- Graphical Method: Plotting ln[A]t vs. t yields a straight line with slope -k
Second-Order Reactions
- Differential Equation: d[A]/dt = -k[A]2
- Integrated Equation: 1/[A]t = kt + 1/[A]0
- Graphical Method: Plotting 1/[A]t vs. t yields a straight line with slope k
Zero-Order Reactions
- Differential Equation: d[A]/dt = -k
- Integrated Equation: [A]t = -kt + [A]0
- Graphical Method: Plotting [A]t vs. t yields a straight line with slope -k
Summary of Plots
- First Order: ln[A] vs. t
- Second Order: 1/[A] vs. t
- Zero Order: [A] vs. t
Reaction Half-Life
- Definition: Time it takes for half of the reactant to be consumed.
- First Order: t1/2 = 0.693/k
- Second Order: t1/2 = 1/k[A]0
- Zero Order: t1/2 = [A]0/2k
Important Open Questions
- Meaning of reaction orders (m, n, p) in a rate law
- Causes of fast vs. slow reaction rates in spontaneous reactions
- Reason for heating reactions
- Temperature's influence on kinetics
Speed of Ants vs. Temperature
- Ants as an Example: Ants' speed increases with temperature.
- Correlation to Chemistry: A similar principle applies to chemical reactions and temperature.
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Description
This quiz covers the essential concepts from Brown Chapter 14 on Chemical Kinetics I. You will explore factors affecting reaction rates, concentration and rate laws, as well as changes in concentration over time. Prepare for challenging questions that test your understanding of chemical kinetics principles.
