Energy and Kinetics in Chemical Reactions

A compilation of key terms and concepts in chemical kinetics, their definitions, and relationships relevant to reactions and rates.

Chemical Kinetics

The study of the rate at which a chemical reaction occurs, the factors that affect the reaction rate, and the reaction mechanism.

Half-life

The time taken for the concentration of a given reactant to reach 50% of its initial concentration.

Reaction Rate

The speed at which a chemical reaction occurs, monitored by how fast products are formed or reactants consumed.

Instantaneous Rate

The rate of reaction at a specific moment, determined by the slope of the tangent at that point.

Average Rate

The rate of reaction calculated over a specified time interval.

Initial Rate

The rate of a reaction at the very start (t = 0) of the reaction.

Rate Law

An expression that describes the relationship between the rate of a chemical reaction and the concentration of its reactants.

Activated Complex

An unstable combination of reactant species representing the highest energy state of a reaction system.

Activation Energy (Eₐ)

The minimum energy necessary for a reaction to occur.

Collision Theory

A model emphasizing the energy and orientation of molecular collisions to explain and predict reaction kinetics.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed.

Molecularity

The number of reactant molecules/particles involved in an elementary reaction.

Reaction Intermediate

A species produced in one step of a mechanism and consumed in a subsequent step.

Frequency Factor (A)

Reflects how well the reaction conditions favor properly oriented collisions between reactant molecules.

Rate-Determining Step (RDS)

The slowest elementary reaction in a mechanism, determining the overall rate of the reaction.

Arrhenius Equation

A mathematical relationship between the rate constant and temperature, expressed as k = A e^{-E_a/RT}.

Integrated Rate Law

An equation that relates the concentration of a reactant to the elapsed time of the reaction.

Zero Order Reaction

A reaction that has a constant rate and is independent of the concentration of the reactant.

First Order Reaction

A reaction where the rate is directly proportional to the concentration of one reactant.

Second Order Reaction

A reaction where the rate is proportional to the square of the concentration of one reactant.

Half-life (t₁/₂) of a Reaction

The time required for one-half of a given amount of reactant to be consumed, varies with reaction order.