IB Chemistry R2.2 How Fast? the Rate of Chemical Change Key Definitions

The activated complex is a high-energy, unstable arrangement of atoms that exists momentarily as reactants are transformed into products. It represents the "peak"; of the energy barrier in a reaction.

Activation energy ($E_a$) is the minimum energy required for colliding particles to form an activated complex (also known as the transition state) and proceed to products.

An equation relating the rate constant $k$ to temperature: $k = Ae^{-\frac{E_a}{RT}}$, where $A$ is the Arrhenius factor, $E_a$ is the activation energy, $R$ is the gas constant, and $T$ is the absolute temperature in kelvin.

The pre-exponential constant $A$ in the Arrhenius equation ($k = Ae^{-E_a/RT}$). It represents the frequency of correctly oriented collisions between reactant particles and has the same units as the rate constant $k$.

An elementary step is a single molecular event in a reaction mechanism where reactants are converted into products or intermediates.

A graph showing how the potential energy of a system changes as a reaction progresses from reactants to products. The horizontal axis shows the reaction coordinate; the vertical axis shows potential energy.

An intermediate is a species that is formed in one elementary step and consumed in another. It is not present in the overall reaction equation because it does not appear in the final products or reactants.

The Maxwell–Boltzmann energy distribution curve provides a visual representation of the distribution of kinetic energies among particles in a system.

The molecularity of an elementary step refers to the number of reacting particles (atoms, ions, or molecules) that must collide simultaneously to drive a chemical change.

The order of a reaction with respect to a reactant is the power to which the concentration of that reactant is raised in the rate equation.

The order of a reaction describes how the concentration of a reactant influences the rate.

Oxidation is the loss of electrons by an atom or ion. It can also refer to the gain of oxygen or the loss of hydrogen.

The rate constant, $ k $, serves as a measure of how fast a reaction proceeds, and it varies with temperature.

The rate equation describes the relationship between the rate of a chemical reaction and the concentrations of the reactants involved.

The rate of reaction measures how quickly reactants are consumed or products are formed during a chemical reaction. It is defined as:

The change in concentration of a reactant or product per unit time.

The slowest step in the mechanism is called the rate-determining step (RDS).

A measure of the progress of a reaction, used as the horizontal axis of an energy profile. It represents the sequence of bond-breaking and bond-forming events from reactants to products.

A transition state represents the highest-energy arrangement of atoms during an elementary step. It is the point where bonds are partially broken and formed, and the system is at the peak of its energy profile.