Chemical Kinetics Flashcards
Define chemical kinetics
Chemical kinetics is the study of the rate at which chemical reactions occur and the factors that affect these rates.
What is reaction rate?
Reaction rate is the change in concentration of a reactant or product per unit time.
Write the general rate equation for a reaction aA + bB → cC + dD.
Rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the reaction orders with respect to A and B.
Define order of reaction
Order of reaction is the sum of the powers of the concentration terms in the rate law equation.
What is a zero-order reaction?
A reaction whose rate is independent of the concentration of the reactants.
Give an example of a first-order reaction.
Radioactive decay is an example of a first-order reaction.
How is the rate constant (k) determined?
The rate constant can be determined experimentally by measuring the rate of reaction at different concentrations of reactants.
What is the integrated rate law for a zero-order reaction?
[A] = [A]₀ - kt
Write the integrated rate law for a first-order reaction.
ln[A] = ln[A]₀ - kt or [A] = [A]₀e^(-kt)
Give the integrated rate law for a second-order reaction.
1/[A] = 1/[A]₀ + kt
Define half-life of a reaction
Half-life is the time required for the concentration of a reactant to decrease to half of its initial concentration.
What is the half-life formula for a first-order reaction?
t₁/₂ = 0.693/k
How does the half-life of a second-order reaction depend on the initial concentration?
t₁/₂ = 1/(k[A]₀), indicating it is inversely proportional to the initial concentration.
State the Arrhenius equation
k = A e^(-Ea/RT), where A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin.
How does the rate constant change with temperature
The rate constant increases with an increase in temperature
What is activation energy?
Activation energy is the minimum energy required for a reaction to occur.
What is the collision theory?
Collision theory states that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation.
Define the transition state
The transition state is a high-energy, unstable state that occurs during the transformation of reactants into products.
Explain the concept of the activated complex.
The activated complex is a temporary, intermediate structure formed during the conversion of reactants into products.
What is a catalyst?
A catalyst is a substance that increases the rate of a reaction without being consumed in the process.
How do catalysts affect activation energy?
Catalysts lower the activation energy of a reaction.
Differentiate between homogeneous and heterogeneous catalysts.
Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase.
What is a reaction mechanism?
A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs.
Define elementary reaction
An elementary reaction is a single step reaction with a single transition state.
What is the rate-determining step?
The rate-determining step is the slowest step in a reaction mechanism that determines the overall reaction rate.
List the factors affecting reaction rates.
Concentration of reactants, temperature, presence of a catalyst, and surface area of reactants.
How does concentration affect reaction rate?
Generally, increasing the concentration of reactants increases the rate of reaction
Why does increasing temperature usually increase reaction rate?
Higher temperatures increase the kinetic energy of molecules, leading to more frequent and energetic collisions.
Explain the effect of surface area on reaction rate
Increasing the surface area of reactants exposes more particles to collisions, increasing the reaction rate.
What is the difference between average rate and instantaneous rate?
The average rate is the change in concentration over a long time interval, while the instantaneous rate is the rate at a specific moment in time.
What is the steady-state approximation?
The steady-state approximation assumes that the concentration of intermediate species remains constant throughout the reaction
Give an example of a pseudo-first-order reaction.
Hydrolysis of esters in the presence of a large excess of water.
What is a rate-determining step in a reaction mechanism?
It is the slowest step in the mechanism that determines the overall rate of the reaction.
Explain the role of a catalyst in the ozone depletion reaction.
Chlorine radicals (Cl•) act as a catalyst in the decomposition of ozone (O3) in the stratosphere
What is the Michaelis-Menten equation in enzyme kinetics?
v = (Vmax[S]) / (Km + [S]), where v is the reaction rate, Vmax is the maximum rate, [S] is the substrate concentration, and Km is the Michaelis constant.
Define molecularity of a reaction
Molecularity is the number of reactant molecules involved in an elementary step of the reaction.
What is the difference between molecularity and order of reaction?
Molecularity is specific to an elementary step and is always an integer, while the order of reaction is determined experimentally and can be fractional.
Describe an example of a second-order reaction.
The reaction 2NO + O2 → 2NO2 is an example of a second-order reaction
What is the Lindemann mechanism?
It is a mechanism to explain unimolecular reactions through a two-step process involving the formation of an energized intermediate.
How is the rate constant for a reaction determined using the Arrhenius plot?
By plotting ln(k) versus 1/T and finding the slope, which is equal to -Ea/R.
What is a chain reaction? Provide an example.
: A chain reaction involves a sequence of reactions where a reactive intermediate regenerates in subsequent steps. Example: the hydrogen-bromine reaction (H2 + Br2 → 2HBr).
