Chemical Kinetics & Catalysis — 60 Terms Defined

Activated Complex Chemical Kinetics & Catalysis kJ/mol The transient arrangement of atoms present at the transition state, poised between reactants and products.

Activation Energy Chemical Kinetics & Catalysis kJ/mol The minimum energy that colliding particles must possess for a reaction to occur. Ea = E(transition state) − E(reactants)

Active Site Chemical Kinetics & Catalysis Dimensionless The specific region of a catalyst or enzyme at which the reacting molecules bind and are transformed.

Adsorption Chemical Kinetics & Catalysis mol/g The accumulation of molecules of a gas or liquid on the surface of a solid.

Arrhenius Equation Chemical Kinetics & Catalysis Various The equation describing how a rate constant varies with temperature and activation energy. k = A e^(−Ea/RT)

Autocatalysis Chemical Kinetics & Catalysis Dimensionless Catalysis of a reaction by one of its own products.

Average Rate Chemical Kinetics & Catalysis mol/(L·s) The overall change in concentration divided by the total time interval over which it occurred. rate_avg = Δ[A] / Δt

Bimolecular Reaction Chemical Kinetics & Catalysis L/(mol·s) An elementary step in which two species collide and react. A + B → products, rate = k[A][B]

Catalysis Chemical Kinetics & Catalysis Dimensionless The process by which a reaction rate is increased through the action of a catalyst.

Catalyst Chemical Kinetics & Catalysis Dimensionless A substance that increases the rate of a reaction by providing an alternative pathway of lower activation energy, without being consumed.

Catalyst Poisoning Chemical Kinetics & Catalysis Dimensionless The loss of catalytic activity caused by a substance binding irreversibly to the active sites.

Chain Reaction Chemical Kinetics & Catalysis Dimensionless A self-sustaining reaction sequence in which a reactive intermediate regenerates itself at each cycle. initiation → propagation → termination

Chemical Kinetics Chemical Kinetics & Catalysis mol/(L·s) The study of reaction rates, the factors that influence them, and the step-by-step mechanisms by which reactions occur.

Chemisorption Chemical Kinetics & Catalysis kJ/mol Strong adsorption in which actual chemical bonds form between the adsorbate and the surface. ΔH ≈ −80 to −400 kJ/mol

Collision Frequency Chemical Kinetics & Catalysis s⁻¹ The number of collisions occurring per unit volume per unit time in a reacting mixture. Z ∝ n²σ√T

Collision Theory Chemical Kinetics & Catalysis mol/(L·s) The model that explains reaction rates in terms of the frequency, energy and orientation of collisions between reacting particles. rate = pZ e^(−Ea/RT)

Complex Reaction Chemical Kinetics & Catalysis Dimensionless An overall reaction that proceeds through two or more elementary steps.

Effective Collision Chemical Kinetics & Catalysis Dimensionless A collision that actually leads to reaction because it has both sufficient energy and correct orientation.

Elementary Reaction Chemical Kinetics & Catalysis Dimensionless A reaction that occurs in a single step exactly as written, with no detectable intermediate. order = molecularity

Energy Profile Diagram Chemical Kinetics & Catalysis kJ/mol A plot of potential energy against reaction coordinate showing reactants, transition states, intermediates and products.

Enzyme Catalysis Chemical Kinetics & Catalysis Dimensionless Catalysis by protein molecules that bind substrates at a specific active site and lower the activation energy dramatically.

First-Order Reaction Chemical Kinetics & Catalysis s⁻¹ A reaction whose rate is directly proportional to the concentration of a single reactant. ln[A] = ln[A]₀ − kt

Free Radical Chain Mechanism Chemical Kinetics & Catalysis Dimensionless A chain mechanism in which the propagating intermediates are species bearing unpaired electrons. X· + RH → HX + R·

Freundlich Adsorption Isotherm Chemical Kinetics & Catalysis mol/g An empirical relation describing adsorption on heterogeneous surfaces with a distribution of site energies. x/m = k p^(1/n)