Chem 2 kinetics

Periodic Rate of Reaction

Calculated by dividing the change in concentration by a specific, measurable time period.

Instantaneous Rate of Reaction

The reaction rate at a specific moment in time; calculated from the slope of a tangent on a concentration vs. time graph.

Normalised Rate

The measured rate of a species divided by its stoichiometric coefficient in the balanced equation.

Rate Equation

An experimentally determined formula linking reaction rate to reactant concentrations: $rate = k[A]^x[B]^y$

Molecularity

The number of reactant molecules involved in a single simple reaction step (e.g., unimolecular, bimolecular).

Simple Reaction

A reaction that occurs in a single step exactly as it is written.

Sequential (Complex) Reaction

A reaction that occurs in a series of simple steps (a reaction mechanism).

Rate Determining Step (RDS)

The slowest step in a multi-step reaction mechanism; it dictates the overall rate equation.

Order of Reaction

The power to which a specific reactant's concentration is raised in the experimentally determined rate equation.

Initial Rates Method

A technique to find reaction orders by running the reaction multiple times with different initial concentrations and comparing the initial rates.

Integrated Rate Equations

Formulas used to graph concentration vs. time to find reaction order. Straight lines occur for $[A]$ (0th), $\ln[A]$ (1st), or $1/[A]$ (2nd).

Half-life

The time required for exactly half of the original reactant to be consumed. It is only constant for 1st order reactions.

Arrhenius Equation

$k = A e^{-E_a / RT}$; shows that the rate constant increases exponentially as temperature rises or activation energy lowers.

Activation Energy ($E_a$)

The minimum amount of energy required for a collision to result in a successful chemical reaction.

Catalyst

A substance that increases reaction rate by providing an alternative pathway with a lower activation energy, without being consumed.

Homogeneous vs. Heterogeneous Catalyst

Homogeneous catalysts operate in the same phase as the reactants; heterogeneous catalysts operate in a different phase.