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Questions and Answers
For a hypothetical elementary reaction $A + 2B \rightarrow C$, what is the rate law?
For a hypothetical elementary reaction $A + 2B \rightarrow C$, what is the rate law?
- Rate = $k[A][B]$
- Rate = $k[A][B]^2$ (correct)
- Rate = $k[A]^2[B]$
- Rate = $k[C]$
Consider a reaction mechanism with the following steps:
Step 1: $A + B \rightleftharpoons I$ (fast equilibrium)
Step 2: $I + C \rightarrow P$ (slow)
What is the predicted rate law for the overall reaction?
Consider a reaction mechanism with the following steps:
Step 1: $A + B \rightleftharpoons I$ (fast equilibrium) Step 2: $I + C \rightarrow P$ (slow)
What is the predicted rate law for the overall reaction?
- Rate = $k[A][B][C]$ (correct)
- Rate = $k[P]$
- Rate = $k[C]$
- Rate = $k[A][B]$
The rate constant of a reaction is found to increase by a factor of 4 when the temperature is increased from 300 K to 360 K. Calculate the activation energy ($E_a$) of the reaction, assuming the Arrhenius equation is valid. (R = 8.314 J/mol·K)
The rate constant of a reaction is found to increase by a factor of 4 when the temperature is increased from 300 K to 360 K. Calculate the activation energy ($E_a$) of the reaction, assuming the Arrhenius equation is valid. (R = 8.314 J/mol·K)
- $E_a$ = 80 kJ/mol
- $E_a$ = 20 kJ/mol
- $E_a$ = 40 kJ/mol (correct)
- $E_a$ = 60 kJ/mol
A certain reaction has an activation energy of 50 kJ/mol. By what factor will the rate constant increase when the temperature is raised from 298 K to 308 K? (R = 8.314 J/mol·K)
A certain reaction has an activation energy of 50 kJ/mol. By what factor will the rate constant increase when the temperature is raised from 298 K to 308 K? (R = 8.314 J/mol·K)
A catalyst increases the rate of a chemical reaction by...
A catalyst increases the rate of a chemical reaction by...
Consider a reaction with the rate law: rate = $k[A]^2[B]$. If the concentration of A is doubled and the concentration of B is halved, by what factor will the reaction rate change, assuming temperature remains constant?
Consider a reaction with the rate law: rate = $k[A]^2[B]$. If the concentration of A is doubled and the concentration of B is halved, by what factor will the reaction rate change, assuming temperature remains constant?
The reaction $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ exhibits a rate law of the form rate = $k[NO]^2[O_2]$. If the volume of the reaction vessel is suddenly reduced to one-third of its original volume, by what factor will the reaction rate increase?
The reaction $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ exhibits a rate law of the form rate = $k[NO]^2[O_2]$. If the volume of the reaction vessel is suddenly reduced to one-third of its original volume, by what factor will the reaction rate increase?
For a first-order reaction, what percentage of the reactant will remain after two half-lives?
For a first-order reaction, what percentage of the reactant will remain after two half-lives?
A certain reaction is found to have a rate constant, $k$, that increases with temperature. Which of the following conclusions can be drawn from this observation?
A certain reaction is found to have a rate constant, $k$, that increases with temperature. Which of the following conclusions can be drawn from this observation?
The decomposition of $N_2O_5(g)$ follows first-order kinetics. Given that the rate constant $k = 5.0 × 10^{-4} s^{-1}$ at a certain temperature, calculate the half-life of $N_2O_5(g)$ in minutes.
The decomposition of $N_2O_5(g)$ follows first-order kinetics. Given that the rate constant $k = 5.0 × 10^{-4} s^{-1}$ at a certain temperature, calculate the half-life of $N_2O_5(g)$ in minutes.
For the elementary step $A + 2B \rightarrow C$, what is the molecularity and the rate law?
For the elementary step $A + 2B \rightarrow C$, what is the molecularity and the rate law?
A reaction has an activation energy of 75 kJ/mol. By what factor will the rate constant increase when the temperature is raised from 25°C to 50°C?
A reaction has an activation energy of 75 kJ/mol. By what factor will the rate constant increase when the temperature is raised from 25°C to 50°C?
Flashcards
Chemical Kinetics
Chemical Kinetics
The study of reaction speeds, influencing factors, and reaction mechanisms.
Reaction Rate
Reaction Rate
The speed at which reactants change into products.
Rate Law
Rate Law
Expresses the relationship between reaction rate and reactant concentrations.
Rate Constant (k)
Rate Constant (k)
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Reaction Order
Reaction Order
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Integrated Rate Laws
Integrated Rate Laws
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Half-Life (t1/2)
Half-Life (t1/2)
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Zero-Order Reaction
Zero-Order Reaction
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Reaction Mechanism
Reaction Mechanism
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Rate-Determining Step
Rate-Determining Step
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Activation Energy (Ea)
Activation Energy (Ea)
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Catalyst
Catalyst
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Study Notes
- Chemical kinetics studies reaction rates, the factors affecting them, and reaction mechanisms
- It gives insight into the rate at which reactants convert to products, and the sequence of elementary steps involved
Reaction Rate
- Reaction rate refers to the speed at which reactants convert to products
- Reaction rate is typically expressed as the change in concentration of a reactant or product per unit of time, such as M/s
- Factors that influence reaction rate include concentration, temperature, the presence of a catalyst, and surface area
- Reaction rate changes over time and usually slows down as reactants are consumed
Rate Laws
- Rate laws express the relationship between the rate of a reaction and the concentrations of the reactants
- Rate laws are experimentally determined
- The general form of a rate law is: rate = k[A]^m[B]^n, where [A] and [B] are the concentrations of reactants, m and n are the reaction orders with respect to A and B, and k is the rate constant
- Overall reaction order equals the sum of the individual orders (m + n)
- The rate constant (k) is a proportionality constant reflecting a reaction's intrinsic speed
- The rate constant's value depends on temperature and the presence of a catalyst
- Reaction order indicates how the rate is affected by the concentration of each reactant
- First-order reaction rates are proportional to the concentration of one reactant, expressed as rate = k[A]
- Second-order reaction rates are proportional to the square of the concentration of one reactant (rate = k[A]^2) or the product of the concentrations of two reactants (rate = k[A][B])
- Zero-order reactions have a constant rate that is independent of the concentration of reactants, expressed as rate = k
Integrated Rate Laws
- Integrated rate laws relate the concentration of reactants to time
- They are derived from differential rate laws using calculus.
- Integrated rate laws are used to determine reactant concentration at a given time, or the time needed for a certain amount of reactant to be consumed
- For a first-order reaction: ln[A]t - ln[A]0 = -kt or ln([A]t/[A]0) = -kt, where [A]t is the concentration at time t, [A]0 is the initial concentration, and k is the rate constant
- For a second-order reaction: 1/[A]t - 1/[A]0 = kt
- For a zero-order reaction: [A]t - [A]0 = -kt
Half-Life
- Half-life (t1/2) is the time it takes for the concentration of a reactant to decrease to one-half of its initial value
- For a first-order reaction, t1/2 = 0.693/k, which is independent of the initial concentration
- For a second-order reaction, t1/2 = 1/(k[A]0), which depends on the initial concentration
- For a zero-order reaction, t1/2 = [A]0/(2k), which also depends on the initial concentration
Reaction Mechanisms
- A reaction mechanism refers to the step-by-step sequence of elementary reactions by which an overall chemical change occurs
- Elementary reactions are single-step reactions that cannot be broken down into simpler steps
- The rate law for an elementary reaction can be written directly from the reaction's stoichiometry
- The molecularity of an elementary reaction is the number of reactant molecules involved in the step (e.g., unimolecular, bimolecular, or termolecular)
- The rate-determining step is the slowest step in the mechanism, which determines the overall reaction rate
Activation Energy
- Activation energy (Ea) is the minimum energy needed for reactants to overcome the energy barrier and form products.
- It is the energy difference between the reactants and the transition state (activated complex)
- The Arrhenius equation relates the rate constant (k) to the activation energy (Ea) and temperature (T): k = Ae^(-Ea/RT), where A is the frequency factor and R is the gas constant (8.314 J/mol·K)
- The frequency factor (A) represents the frequency of collisions with proper orientation
- Higher activation energy corresponds to a slower reaction rate, while a higher temperature leads to a faster reaction rate
- Catalysts lower the activation energy
Catalysis
- A catalyst is a substance that increases the rate of a reaction without being consumed
- Catalysts provide an alternative reaction pathway with a lower activation energy
- Homogeneous catalysts exist in the same phase as the reactants, while heterogeneous catalysts exist in a different phase
- Enzymes are biological catalysts that demonstrate high specificity and efficiency
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Description
Explore chemical kinetics, focusing on reaction rates and the factors influencing them. Understand how rate laws describe the relationship between reactant concentrations and reaction speed. Learn about the experimental determination of rate laws.
