CHEM122 Chemical Kinetics

State Function

A function that describes the equilibrium state of a system and does not depend on how the system arrived at its current state.

Path Function

A function that depends on the specific path taken to move from one state to another.

Kinetics

The study of the rates of chemical reactions.

Thermodynamics

The branch of physical science that deals with the relationships between heat and other forms of energy.

Activation Energy

The minimum energy required for a chemical reaction to occur.

Rate Law

An equation that relates the rate of a reaction to the concentration of its reactants.

Instantaneous Rate

The rate of reaction at a specific point in time, determined by the slope of the tangent to the curve of concentration versus time.

Differential Rate Law

A mathematical expression that relates reaction rate to concentration, often written as Rate = -d[A]/dt = k[A]^n.

Integrated Rate Law

An equation that expresses the concentration of reactants as a function of time.

Half-Life

The time required for the concentration of a reactant to decrease to half of its initial value.

First Order Reaction

A reaction where the rate is directly proportional to the concentration of one reactant.

Second Order Reaction

A reaction where the rate is proportional to the square of the concentration of one reactant or to the product of the concentrations of two reactants.

Zero Order Reaction

A reaction where the rate is independent of the concentration of reactants.

Pseudo-Rate Law

A simplification of a rate law used when one reactant is present in a large excess compared to others.

Steady-State Approximation

An assumption that the concentration of intermediate species in a reaction mechanism remains constant over time.

Collision Theory

The theory that states that for a reaction to occur, reactants must collide with sufficient energy and proper orientation.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed in the process.

Arrhenius Equation

An equation that shows the relationship between the rate constant, activation energy, and temperature.

Elementary Reaction

A single step in a reaction mechanism that represents a single molecular event.

Reaction Mechanism

The step-by-step sequence of elementary reactions by which overall chemical change occurs.

Transition State

The highest energy state along the reaction coordinate, representing the point of maximum potential energy.

Chain Reaction

A series of reactions where the products of one step initiate further reactions.

Maxwell-Boltzmann Distribution

A statistical distribution of particle speeds in a gas, reflecting the energy distribution of particles.

Order of Reaction

The power to which the concentration of a reactant is raised in the rate law equation.

Rate Constant (k)

A constant that is specific to a particular reaction at a given temperature, appearing in the rate law.

Activation Complex

A transient, high-energy structure formed during the collision of reactants in a chemical reaction.

Factors Affecting Reaction Rates

Concentration, temperature, surface area, and presence of catalysts can affect the rates of chemical reactions.

Temperature Dependency

As temperature increases, reaction rates generally increase due to higher kinetic energy and collision frequency.

Heterogeneous Reaction

A reaction involving reactants in different phases, such as solid and gas.

Homogeneous Reaction

A reaction where all reactants and products are in the same phase.

Dynamic Equilibrium

A state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction.

Zero-Order Reaction Characteristics

In zero-order reactions, the rate is constant and does not depend on reactant concentrations.

Mechanistic Studies

The investigation of the detailed steps and pathways in a chemical reaction mechanism.

Chemical Rate Law

An equation that expresses the rate of a chemical reaction as a function of the concentration of its reactants.

Overall Order of Reaction

The sum of the powers of the concentration terms in the rate law.

Rate Law Expression

A mathematical formula that defines the relationship between reactant concentration and the rate of the reaction.

Rate Equation for Second Order Reaction

For a single reactant: Rate = k[A]^2; or two reactants: Rate = k[A][B].

Integrated Rate Law for First Order

ln[A] = -kt + ln[A]0, describing concentration of a reactant over time for first-order reactions.

Integrated Rate Law for Second Order

1/[A] = kt + 1/[A]0, describing concentration over time for second-order reactions.

Arrhenius Parameters

Parameters in the Arrhenius equation including the activation energy (Ea) and the pre-exponential factor (A).

Temperature Influence on Rate Constants

Rate constants generally increase with temperature, increasing reaction rates due to more frequent collisions.

Mechanism of Rate Determination

The slowest elementary step in a reaction mechanism determines the rate of the overall reaction.

Pseudo-First Order Reaction

A situation where a reaction appears to be first order due to one reactant being much more concentrated than the other.

What is a Rate Law?

An equation that relates the rate of a chemical reaction to the concentration of its reactants.

What factors affect the rate of a reaction?

Concentration, temperature, surface area, and catalysts.

How is the rate of a reaction typically represented?

The rate of a reaction is often given as change in concentration per unit time.

What does the rate constant (k) represent?

A value that is specific to a particular reaction at a given temperature.

What is the order of a reaction?

The sum of the powers of the concentrations of the reactants in the rate law.

What are zero-order reactions characterized by?

The reaction rate is constant and independent of the concentration of reactants.

How do first-order reactions behave?

The rate of reaction is directly proportional to the concentration of one reactant.

What distinguishes second-order reactions?

The rate is proportional to the square of the concentration of one reactant or the product of two reactants' concentrations.

What is a pseudo-first-order reaction?

A reaction that appears to be first order because one reactant is in large excess.

What does the term 'half-life' refer to in kinetics?

The time required for the concentration of a reactant to decrease to half its initial value.

What is the significance of the Arrhenius equation?

It shows the relationship between temperature, activation energy, and the rate constant.

What is activation energy (Ea)?

The minimum energy required for a chemical reaction to occur.

What is meant by 'dynamic equilibrium' in reaction kinetics?

A state where the rates of the forward and reverse reactions are equal.

What is the Integrated Rate Law for a first-order reaction?

ln[A] = -kt + ln[A]0.

How do temperature and rate constants relate?

Generally, as the temperature increases, the rate constants increase, leading to faster reaction rates.