Unit Summary Package - Reaction Rates and Mechanisms

These flashcards cover key vocabulary and definitions related to reaction rates and mechanisms, facilitating study and understanding of the concepts in chemistry.

Reaction Rate

The change in concentration of a reactant or product per unit time, usually expressed in mol·L⁻¹·s⁻¹.

Average Rate

Calculated over an interval of time; defined as the slope of the secant line that intersects data at two points.

Instantaneous Rate

The rate at a specific time on the curve; defined as the slope of the tangent line that intersects data at one point.

Collision Theory

States that for a reaction to occur, particles must collide with enough energy and proper orientation.

Activation Energy (Ea)

The minimum energy barrier that must be overcome for a reaction to produce products.

Transition State

The highest energy state during a reaction.

Catalyst

A substance that enhances the rate of a reaction by providing an alternative pathway with lower activation energy.

Elementary Step

A single step in a reaction mechanism involving one or more reactants.

Reaction Mechanism

The complete sequence of elementary steps that lead to the overall reaction.

Rate-determining Step

The slowest elementary step in a reaction mechanism that limits the overall reaction rate.

Reaction Intermediate

A substance produced in one elementary step and consumed in another; does not appear in the overall reaction.

Concentration's Effect on Reaction Rate

Greater concentration increases the frequency of collisions, raising the probability of effective collisions.

Temperature's Effect on Reaction Rate

Higher temperature increases kinetic energy, leading to more frequent and effective particle collisions.

Surface Area's Effect on Reaction Rate

Lesser particle size increases surface area, leading to more exposure for collisions in solid-gas or solid-liquid reactions.

Nature of Reactants

Ionic reactions are typically faster than covalent; strong bonds reduce reaction rates.

Rate Law

An equation showing the relationship between the rate of a reaction and the concentration of reactants.

First Order Reaction

A reaction whose rate depends linearly on the concentration of one reactant.

Second Order Reaction

A reaction whose rate depends on the square of the concentration of one reactant or the product of the concentrations of two reactants.

Total Order

The sum of the exponents in a rate law.

Stoichiometric Rates

Rates of reaction measured based on a balanced chemical equation.

Half-Life

The time required for the concentration of a reactant to decrease to half of its initial value.

First-Order Half-Life Formula

t1/2 = 0.693/k, where k is the rate constant.

Potential Energy Diagram

A graphical representation showing the energy changes during a reaction, including reactants, products, and activation energy.

Exothermic Reaction

A reaction that releases energy, resulting in products having lower energy than the reactants.

Endothermic Reaction

A reaction that absorbs energy, resulting in products having higher energy than the reactants.

Catalyzed Pathway

A reaction pathway that has a lower activation energy due to the presence of a catalyst.

Uncatalyzed Pathway

A reaction pathway where no catalyst is present, usually with higher activation energy.

Experimental Rate Law

The rate law determined through experimental methods that outlines how rate is affected by concentrations.

Rate Laws from Reaction Mechanisms

Defined using the rate determining step and must match experimentally determined rate laws.

Collision Efficiency

The effectiveness with which colliding reactants come together to form products.

Molecularity

The number of reactant particles involved in an elementary step.

Kinetic Energy

The energy possessed by an object due to its motion, impacting collision effectiveness.

Reaction Conditions

Factors such as temperature, concentration, and pressure that influence the reaction rate.

Rate Constant (k)

A proportionality constant that relates the rate of a reaction to the concentrations of reactants in the rate law.

Mechanism Requirements

For a proposed mechanism to be valid, it must sum to the overall reaction and agree with experimental data.

Arrhenius Equation

An equation that relates the rate constant k to temperature and activation energy.