Kinetics Flashcards
What is the definition of the rate of reaction?
The rate of reaction is the change in concentration of a reactant or product per unit time, usually measured in mol dm⁻³ s⁻¹.
How can the rate of a reaction be calculated?
Rate = change in concentration ÷ time, or expressed mathematically as: rate = Δ[concentration] ÷ Δtime.
What does collision theory state?
Collision theory states that particles must collide with sufficient energy (activation energy) and with the correct orientation for a reaction to occur.
What is activation energy?
Activation energy (Ea) is the minimum amount of energy that colliding particles need to have for a reaction to occur.
How does increasing temperature affect the rate of reaction?
Increasing temperature increases the kinetic energy of particles, leading to more frequent and successful collisions, which increases the rate of reaction.
Why does increasing the concentration of reactants increase the rate of reaction?
Higher concentration means more particles per unit volume, leading to more frequent collisions and a higher chance of successful collisions.
How does increasing pressure affect the rate of a reaction involving gases?
Increasing pressure forces gas particles closer together, increasing the frequency of collisions and hence increasing the rate of reaction.
What effect does a catalyst have on the rate of reaction?
A catalyst provides an alternative reaction pathway with a lower activation energy, increasing the rate of reaction without being used up.
How do catalysts affect the energy distribution of particles?
Catalysts lower the activation energy, so a greater proportion of particles have sufficient energy to overcome the activation barrier and react successfully.
What is the Maxwell-Boltzmann distribution?
The Maxwell-Boltzmann distribution shows the distribution of energies of molecules in a gas at a given temperature.
Why does the Maxwell-Boltzmann distribution start at the origin?
No particles have zero energy, so the graph starts at the origin (0,0).
How does temperature affect the Maxwell-Boltzmann distribution?
At higher temperatures, the curve shifts to the right, becomes flatter, and more particles have energy greater than the activation energy.
What happens to the area under the curve in a Maxwell-Boltzmann distribution when temperature increases?
The area under the curve remains the same because it represents the total number of particles, which does not change.
Why does a small increase in temperature cause a large increase in reaction rate?
A small increase in temperature significantly increases the number of particles with energy greater than the activation energy, resulting in more successful collisions.
What is a heterogeneous catalyst?
A heterogeneous catalyst is in a different phase from the reactants, typically a solid catalyst with gaseous or liquid reactants.
What is a homogeneous catalyst?
A homogeneous catalyst is in the same phase as the reactants, often forming an intermediate species.
What is a rate equation?
The rate equation shows how the rate of reaction depends on the concentration of reactants. It is of the form: Rate = k[A]ᵐ[B]ⁿ, where m and n are the orders.
What is the rate constant (k)?
The rate constant (k) is a proportionality constant that links the rate of reaction to the concentration of reactants raised to their respective powers.
How is the overall order of a reaction determined?
The overall order of a reaction is the sum of the powers of the concentration terms in the rate equation (m + n).
What is the order of reaction with respect to a reactant?
The order of reaction with respect to a reactant is the power to which its concentration is raised in the rate equation.
How does the rate of reaction change in a zero-order reaction?
In a zero-order reaction, the rate is independent of the concentration of the reactant. Rate = k.
How does the rate of reaction change in a first-order reaction?
In a first-order reaction, the rate is directly proportional to the concentration of the reactant. Rate = k[A].
How does the rate of reaction change in a second-order reaction?
In a second-order reaction, the rate is proportional to the square of the concentration of the reactant. Rate = k[A]².
How can the order of a reaction be determined experimentally?
The order of reaction can be determined by the initial rates method or by plotting concentration-time graphs and analyzing the gradients.
What is a half-life (t₁/₂) in the context of reaction kinetics?
The half-life is the time taken for the concentration of a reactant to halve.
What is the characteristic of a first-order reaction in terms of half-life?
A first-order reaction has a constant half-life, independent of concentration.
How can rate constants be calculated from half-life data?
For a first-order reaction: k = ln(2) ÷ t₁/₂.
What is the Arrhenius equation?
The Arrhenius equation is: k = Ae^(-Ea/RT), where k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is temperature in Kelvin.
How does a graph of ln(k) against 1/T relate to the Arrhenius equation?
A graph of ln(k) against 1/T gives a straight line with a gradient of -Ea/R and an intercept of ln(A).
What is the significance of the pre-exponential factor (A) in the Arrhenius equation?
The pre-exponential factor accounts for the frequency of collisions and the orientation of reactants, representing the maximum possible rate if all collisions were successful.
How can the rate of a reaction be measured experimentally?
The rate can be measured by monitoring changes in reactant or product concentrations over time using methods like gas volume, mass change, or color change.
How can gas volume be used to measure rate?
The volume of gas produced is measured over time using a gas syringe.
How can mass loss be used to measure rate?
The decrease in mass is measured when a gas is released, often using a balance.
How can color change be used to measure rate?
A colorimeter is used to measure the change in absorbance during a reaction involving colored species.
How can pH change be used to measure rate?
A pH meter is used to monitor changes in pH during acid-base reactions.
How can time for a precipitate to form be used to measure rate?
The time taken for a cross to disappear when a precipitate forms can be measured.
How can titration be used to measure rate?
Samples are taken at regular intervals, quenched, and titrated to determine the concentration of a reactant or product over time.
