Reaction Kinetics: Reaction Mechanisms
Terms
Activation Energy
-
The difference in energy between the reactants and the transition state
that is the energy barrier
the reactants must overcome to achieve a chemical reaction.
Catalyst
-
A substance that lowers the activation energy for a chemical reaction
without being chemically
altered by the reaction.
Elementary Step
-
A reaction that represents a single collision or intramolecular step in a
reaction mechanism.
Homogeneous Catalyst
-
A catalyst that is in the same phase as the reactants.
Intermediate
-
A species that is both produced and consumed in a chemical reaction. As
such, it does not appear in
the overall reaction but is proposed to be produced in one elementary
step and consumed in
another.
Kinetics
-
The study of the rate and mechanism of chemical reactions.
Mechanism
-
The series of elementary steps that combine to produce the path molecules
take from reactant(s) to
product(s) in a chemical reaction.
Order
-
In the rate law of a reaction, the power to which the concentration of a
reagent is raised. Or, the sum of the powers on the concentration terms in the
rate law.
Rate
-
The speed of a reaction measured in amount or reagent consumed or product
produced per unit time.
Rate Constant
-
The proportionality constant in the rate law expression. This factor
is a measure of the intrinsic
reactivity of the reaction but is not constant with respect to temperature.
Rate Law
-
An expression of the dependence of the rate of a reaction on the
concentrations of reactants.
Rate Limiting Step
-
The slowest elementary step in a mechanism. The rate of the reaction
must
equal the rate of the
slowest step because the reaction can go no faster than its slowest step.
Reaction Coordinate Diagram
-
A plot of free energy versus the reaction coordinate for a reaction that
provides a pictorial
representation of the lowest energy path from reactants to products.
Steady-State Approximation
-
The assumption that the rate of formation and consumption of a highly
reactive intermediate are equal
so that the change in intermediate concentration with respect to time is
approximated to be zero.
Transition State
-
The species with the highest energy between reactants and products on a
reaction coordinate
diagram, it is a short-lived species that represents a combination of
product-like and reactant-like
properties.
