Chemical Kinetics

  • Thermodynamics of reaction
  • Factors affecting reaction rate
  • Rate law expression
  • Reaction order
  • Integrated rate laws

Reaction Rate

  • Definition of reaction rate
  • Units of reaction rate
  • Relationship between concentration and reaction rate
  • Effect of temperature on reaction rate
  • Activation energy

Rate Law Expression

  • Definition of rate law expression
  • Characteristics of rate law expression
  • Determining rate law experimentally
  • Method of initial rates
  • Reaction orders

Reaction Order

  • Definition of reaction order
  • Relation between rate law and reaction order
  • Zero order reactions
  • First order reactions
  • Second order reactions

Integrated Rate Laws

  • Introduction to integrated rate laws
  • Integrated rate law for zero order reactions
  • Integrated rate law for first order reactions
  • Integrated rate law for second order reactions
  • Half-life of a reaction

Reaction Mechanism

  • Definition of reaction mechanism
  • Elementary steps and overall reaction
  • Rate-determining step
  • Reaction intermediates
  • Mechanism and rate law

Temperature and Reaction Rate

  • Collision theory of reaction rates
  • Effect of temperature on reaction rate
  • Arrhenius equation
  • Activation energy and rate constant
  • Catalysts and reaction rate

Catalysts

  • Definition of catalyst
  • Homogeneous catalysts
  • Heterogeneous catalysts
  • Enzymes as biological catalysts
  • Effect of catalysts on reaction rate

Reaction Kinetics and Equilibrium

  • Kinetics and thermodynamics of reactions
  • Relationship between reaction rate and equilibrium constant
  • Equilibrium constant expression
  • Le Chatelier’s principle
  • Effect of temperature and pressure on equilibrium

Factors Affecting Reaction Rate

  • Concentration of reactants
  • Nature of reactants
  • Temperature
  • Catalysts
  • Surface area of reactants
  1. Thermodynamics of Reaction
  • Definition of thermodynamics
  • Laws of thermodynamics
  • Enthalpy (ΔH) and entropy (ΔS)
  • Gibbs free energy (ΔG)
  • Thermodynamic favorability of reactions
  1. Factors Affecting Reaction Rate
  • Concentration of reactants: higher concentrations increase the likelihood of successful collisions
  • Nature of reactants: different reactants have varying reactivity based on their structures and bond strengths
  • Temperature: higher temperatures increase the kinetic energy of molecules, leading to more frequent collisions
  • Catalysts: substances that increase the reaction rate without being consumed in the process
  • Surface area of reactants: smaller particle sizes provide a larger surface area, allowing for more reactive sites
  1. Rate Law Expression
  • Definition of rate law expression: mathematical equation relating the rate of a reaction to the concentrations of reactants
  • Characteristics of rate law expression: specific to each reaction, determined experimentally
  • Determining rate law experimentally: method of initial rates, varying the concentrations of reactants
  • Method of initial rates: measuring reaction rates at different initial concentrations and determining the rate order
  • Reaction orders: the powers of the concentration terms in the rate law expression
  1. Reaction Order
  • Definition of reaction order: the power to which the concentration is raised in the rate law expression
  • Relation between rate law and reaction order: rate law expression provides information on the reaction order
  • Zero order reactions: rate is independent of the concentration of reactants
  • First order reactions: rate is directly proportional to the concentration of a single reactant
  • Second order reactions: rate is directly proportional to the product of the concentrations of two reactants or squared concentration of a single reactant
  1. Integrated Rate Laws
  • Introduction to integrated rate laws: mathematical expressions that relate the concentration of a reactant to time
  • Integrated rate law for zero order reactions: [A] = [A]₀ - kt
  • Integrated rate law for first order reactions: ln([A]/[A]₀) = -kt
  • Integrated rate law for second order reactions: 1/[A] - 1/[A]₀ = kt
  • Half-life of a reaction: the time required for the concentration of a reactant to decrease by half
  1. Reaction Mechanism
  • Definition of reaction mechanism: a series of steps that describes the pathway from reactants to products
  • Elementary steps and overall reaction: elementary steps represent individual molecular events, while the overall reaction is the net result
  • Rate-determining step: the slowest elementary step that determines the overall reaction rate
  • Reaction intermediates: short-lived species formed and consumed during the reaction
  • Mechanism and rate law: the rate law expression is derived from the rate-determining step
  1. Temperature and Reaction Rate
  • Collision theory of reaction rates: reactions occur when molecules collide with sufficient energy and proper orientation
  • Effect of temperature on reaction rate: increase in temperature leads to higher kinetic energy and more successful collisions
  • Arrhenius equation: 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 the temperature in Kelvin
  • Activation energy and rate constant: the minimum energy required for a reaction to occur
  • Catalysts and reaction rate: lower the activation energy, increase the reaction rate
  1. Catalysts
  • Definition of catalyst: substances that increase the rate of a chemical reaction without being consumed in the process
  • Homogeneous catalysts: catalysts in the same phase as the reactants
  • Heterogeneous catalysts: catalysts in a different phase than the reactants
  • Enzymes as biological catalysts: proteins that speed up biochemical reactions in living organisms
  • Effect of catalysts on reaction rate: lower the activation energy, increase the reaction rate
  1. Reaction Kinetics and Equilibrium
  • Kinetics and thermodynamics of reactions: kinetics studies the rate of reactions, while thermodynamics focuses on the favorability
  • Relationship between reaction rate and equilibrium constant: reaction rate determines how quickly equilibrium is reached
  • Equilibrium constant expression: ratio of product to reactant concentrations at equilibrium
  • Le Chatelier’s principle: when a system is at equilibrium, any change will re-establish equilibrium by shifting the reaction in the opposite direction
  • Effect of temperature and pressure on equilibrium: changes in temperature or pressure can shift the equilibrium position
  1. Concentration of Reactants
  • Definition of concentration: the amount of solute present in a given volume of solvent
  • Effect on reaction rate: increased concentration leads to more frequent collisions between reactant molecules, increasing the reaction rate
  • Rate law expression and concentration: rate law expression shows the relationship between reaction rate and reactant concentrations
  • Example: 2A + B -> C, rate = k[A]^2[B]
  • Increase in [A] or [B] increases the rate, while decreasing their concentrations will slow down the reaction
  • Equilibrium and concentration: at equilibrium, the concentrations of reactants and products remain constant, with the forward and backward rates being equal
  1. Nature of Reactants
  • Different reactants have varying reactivity based on their structures and bond strengths
  • Reactants with weaker bonds are more likely to undergo chemical reactions
  • Example: Hydrogen gas (H2) reacts more easily with halogens (e.g., Cl2) compared to inert gases like helium (He)
  1. Temperature and Reaction Rate
  • Increasing temperature increases the kinetic energy of molecules
  • Higher kinetic energy leads to more frequent collisions between reactant molecules
  • Increased collisions result in a higher reaction rate
  • Example: The rate of a reaction may double for every 10°C increase in temperature (known as the “Arrhenius rule”)
  1. Arrhenius Equation
  • Mathematically describes the relationship between temperature and rate constant (k)
  • k = Ae^(-Ea/RT), where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin
  • The Arrhenius equation shows that higher temperatures result in higher rate constants and faster reaction rates
  • Example: The Arrhenius equation can be used to determine the rate of a reaction at different temperatures
  1. Activation Energy
  • Minimum energy required for a reaction to occur
  • Molecules must overcome the activation energy barrier to react
  • Higher activation energy leads to slower reaction rates
  • Catalysts provide an alternative reaction pathway with lower activation energy, increasing the reaction rate
  • Example: Activation energy can be visualized as a hill that reactant molecules need to climb before converting to products
  1. Gibbs Free Energy (ΔG)
  • Thermodynamic quantity that determines the spontaneity and favorability of a reaction
  • ΔG = ΔH - TΔS, where ΔH is the change in enthalpy (heat) and ΔS is the change in entropy (disorder)
  • Negative ΔG indicates a spontaneous and exergonic reaction
  • Positive ΔG indicates a non-spontaneous and endergonic reaction
  • Example: Burning of wood is a spontaneous reaction (negative ΔG) due to the release of heat energy
  1. Thermodynamic Favorability of Reactions
  • ΔG determines the thermodynamic favorability of a reaction
  • If ΔG < 0, the reaction is thermodynamically favorable and proceeds spontaneously
  • If ΔG > 0, the reaction is non-spontaneous and requires an input of energy to proceed
  • Example: The combustion of methane (CH4 + 2O2 -> CO2 + 2H2O) has a negative ΔG, indicating it is thermodynamically favorable
  1. Concentration Effect on Reaction Rate
  • Increasing the concentration of reactants leads to a higher collision frequency
  • More collisions result in more successful collisions and a higher reaction rate
  • Rate law expression incorporates the effect of reactant concentration on reaction rate
  • Example: In the reaction A + B -> C, doubling the concentration of A will double the rate of the reaction
  1. Catalysts and Reaction Rate
  • Catalysts speed up a chemical reaction without being consumed in the process
  • They provide an alternative reaction pathway with a lower activation energy
  • Lower activation energy leads to more reactant molecules having sufficient energy to react
  • Catalysts increase the reaction rate by providing an energetically favorable pathway
  • Example: Enzymes are biological catalysts that facilitate biochemical reactions in living organisms
  1. Surface Area effect on Reaction Rate
  • Breaking solids into smaller particle sizes increases the surface area available for reaction
  • Increasing the surface area allows more reactant molecules to come into contact with each other
  • More collisions occur, resulting in a higher reaction rate
  • Example: Powdered sugar (fine particles) dissolves faster in water compared to a sugar cube (larger surface area)
  1. Equilibrium Constant Expression
  • Equilibrium constant (K) represents the ratio of product to reactant concentrations at equilibrium
  • K = [C]^c/[A]^a[B]^b, where [C], [A], [B] are the concentrations of products and reactants, and a, b, c are the stoichiometric coefficients
  • The value of K indicates the extent of the reaction towards products or reactants
  • Example: For the reaction A + B -> C, the equilibrium constant expression is K = [C]/[A][B]