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Reaction Mechanism
The sequence of events that describes the actual process by which reactants become products; sequence of ELEMENTARY STEPS
Elementary Reaction
Single step in a reaction mechanism.
molecular level
The overall progress of a chemical reaction can be represented at the _____ by a series of simple elementary steps.
Overall Reaction
Net result of all elementary steps combined.
Rate-Determining Step
Slowest step in the sequence of steps leading to product formation.
Molecularity
Number of molecules involved in an elementary step.
Unimolecular
Elementary step involving one molecule.
Bimolecular
Elementary step involving two molecules.
Termolecular
Elementary step involving three molecules.
Rate Law
Expression relating reaction rate to reactant concentrations.
determination of rate law
how stoichiometry can be used when process occurs in one single step
Law of Mass Action
The rate of a simple (one step) reaction is directly proportional to the concentration of the reacting substances.
Reaction Intermediate
Species formed and consumed in a reaction mechanism.
Elementary Step
Process occurring in a single step.
Multistep Mechanism
Reaction involving multiple elementary steps.
Fast Step
Step that occurs quickly in a mechanism.
Slow Step
Step that limits the overall reaction rate.
Equilibrium Step
Step involving forward and reverse reactions.
Stoichiometry
Relationship between reactants and products in a reaction.
Effective Collision
Collision leading to a reaction.
Plausible Mechanism
Mechanism consistent with experimental rate laws.
Intermediates
species that appear in reaction mechanism but not in the overall balanced equation
Elementary Process
Simple reaction step leading to product formation.
Rate Law for Elementary Steps
Derived directly from the stoichiometry of the step.
NO3 Intermediate
Species formed in a slow step, consumed later.
Intermediate Species
Unstable species formed and consumed in reactions.
Slow Initial Step
reaction occurs in two steps
Fast Initial Step
First step in a reaction mechanism, often rapid.
Equilibrium
State where forward and reverse reactions balance.
Rate-determining Step
Slowest step that limits overall reaction rate.
cannot occur faster
The overall reaction ______ than this slowest, rate-determining step.
Activation Energy (Ea)
Minimum energy required for a reaction to occur.
Transition State
High-energy state during bond breaking and forming.
Kinetic Energy
Energy of motion required for molecular collisions.
Exothermic Reaction
Reaction releasing energy, products lower in energy.
Endothermic Reaction
Reaction absorbing energy, products higher in energy.
Rate Equation
Mathematical expression for reaction rate based on concentrations.
Concentration
Amount of substance in a given volume.
Bond Breakage
Process requiring energy to separate atoms in reactants.
Energy Barrier
Energy threshold that must be overcome for reaction.
Reaction Rate
Speed at which reactants convert to products.
Molecular Collisions
Interactions between molecules that can lead to reactions.
Chemical Equation
Symbolic representation of a chemical reaction.
Rate Constant (k)
Proportionality factor in the rate law expression.
Kinetic Molecular Theory
Temperature increase raises total kinetic energy.
Activation Energy (Ea)
Minimum energy needed to start a chemical reaction.
Exothermic Reaction
Releases energy, typically heat, during reaction.
Endothermic Reaction
Absorbs energy from surroundings during reaction.
Energy Diagram
Graphical representation of energy changes in reactions.
Delta H
Change in enthalpy during a chemical reaction.
Arrhenius Equation
Mathematical relationship between rate constant and activation energy.
Frequency Factor (A)
Probability of effective collisions in a reaction.
Rate Constant (k)
Proportionality constant in the Arrhenius equation.
Gas Constant (R)
8.314 J/K•mol, used in Arrhenius equation.
Temperature (T)
Measured in Kelvin, affects reaction rates.
Maxwell-Boltzmann Distribution
Describes distribution of kinetic energies in molecules.
Kinetic Energy
Energy possessed by molecules due to motion.
Catalyst
Substance that increases reaction rate without consumption.
Heterogeneous Catalyst
Catalyst in a different phase than reactants.
Homogeneous Catalyst
Catalyst in the same phase as reactants.
Effective Collisions
Collisions that lead to a chemical reaction.
All at once or several discrete steps
Reaction mechanism may occur....
Intermediate
Transient species formed during a reaction pathway.
Temperature Dependence
Rate constant varies with temperature changes.
Natural Logarithm
Mathematical function used in Arrhenius equation transformation.
Activation Energy Barrier
Energy threshold that reactants must overcome.
Heterogeneous Catalyst
Catalyst in solid form with gaseous reactants/products.
Adsorption
Binding of reactant molecules to catalyst surface.
Active Sites
Locations on catalyst surface for reactant binding.
Catalytic Converter
Device using catalysts to reduce vehicle emissions.
Ethylene
C2H4, a gaseous reactant in hydrogenation.
Hydrogenation
Addition of hydrogen to unsaturated compounds.
Turnover Number
Catalytic events per unit time at active site.
Enzyme
Biological catalyst facilitating biochemical reactions.
Substrate
Reactant that binds to an enzyme's active site.
Enzyme Inhibitor
Molecule blocking enzyme's active site.
Nitrogenase
Enzyme converting nitrogen gas to ammonia.
Ostwald Process
Industrial method for producing nitric acid.
Intermediate
Species formed during a reaction, not in products.
Catalyst Efficiency
Measure of how effectively a catalyst speeds up reactions.
Metal Catalysts
Common catalysts like Ni, Pt, or Pd.
Biological Systems
Natural environments where enzymes act as catalysts.
Specificity of Enzymes
Enzymes catalyze specific reactions only.
Molecular Mass of Enzymes
Typically ranges from 10,000 to 1,000,000 amu.
Desorption
Release of products from the catalyst surface.
Gaseous Reactants
Reactants in gas phase participating in reactions.
Note 
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