Chemical Thinking: Kinetics, Reaction Mechanisms, and Thermodynamics

Vocabulary practice flashcards covering chemical kinetics, integrated rate laws, reaction mechanisms, catalysis, stereochemistry, and chemical thermodynamics based on lecture materials.

Brønsted-Lowry Acid

A substance that donates a proton ($\text{H}^+$) to another chemical species in a reaction.

Brønsted-Lowry Base

A substance that accepts a proton ($\text{H}^+$) from another chemical species.

Carboxylic Acid Functional Group

An acidic organic functional group consisting of a carbonyl group bonded to a hydroxyl group ($-\text{COOH}$), which readily transfers its proton in aqueous solution.

Amine Functional Group

A basic organic functional group containing a nitrogen atom with a lone pair ($-\text{NH}_2$, $-\text{NHR}$, or $-\text{NR}_2$) that can act as a proton acceptor.

Average Reaction Rate

The change in reactant or product concentration divided by the finite time interval over which that change occurs: $\text{Rate}_{\text{Average}} = -\frac{\Delta [\text{R}]}{\Delta t} = \frac{\Delta [\text{P}]}{\Delta t}$.

Instantaneous Reaction Rate

The reaction rate at a specific moment in time, given by the negative slope of the concentration versus time curve: $\text{Rate}_{\text{Inst}} = -\frac{d[\text{R}]}{dt}$.

Kinetic Stability

A property describing how slowly a substance decomposes or reacts, determined by the magnitude of the activation energy barrier and decreasing as temperature ($T$) increases.

Rate Law

An equation relating reaction rate to the rate constant ($k$) and reactant concentrations raised to powers representing reaction orders: $\text{Rate} = k[\text{A}]^x[\text{B}]^y$.

Zeroth-Order Reaction

A process whose rate is completely independent of reactant concentration ($\text{Rate} = k$), producing a linear plot of $[\text{R}]$ versus time with slope $m = -k$.

First-Order Integrated Rate Law

The mathematical expression $\ln[\text{R}] = \ln[\text{R}]_0 - kt$ (or $[\text{R}] = [\text{R}]_0 e^{-kt}$), showing that a plot of $\ln[\text{R}]$ versus time yields a straight line with slope $m = -k$.

Second-Order Integrated Rate Law

The mathematical expression $\frac{1}{[\text{R}]} = \frac{1}{[\text{R}]_0} + kt$, showing that a plot of $\frac{1}{[\text{R}]}$ versus time yields a straight line with slope $m = k$.

Half-Life ($t_{1/2}$)

The time required for the concentration of a reacting substance to decrease to exactly half of its initial value.

Integrated Rate Law Summary

The systematic mathematical relationships and linear plotting coordinates for zeroth-, first-, and second-order reactions and their associated half-lives ($t_{1/2} = \frac{[\text{R}]_0}{2k}$, $t_{1/2} = \frac{\ln(2)}{k}$, and $t_{1/2} = \frac{1}{k[\text{R}]_0}$).

Arrhenius Equation

An equation expressing the temperature dependence of the rate constant: $k = A e^{-E_a/(RT)}$, or linearly $\ln(k) = -\frac{E_a}{R}\left(\frac{1}{T}\right) + \ln(A)$, where the slope is $m = -\frac{E_a}{R}$.

Activation Energy ($E_a$)

The minimum kinetic energy that colliding reactant molecules must possess to overcome the energetic barrier and form the transition state.

Collision Theory

A model stating that chemical reactions occur only when reacting particles collide with sufficient energy ($\ge E_a$) and appropriate spatial orientation.

Elementary Step

A single molecular event or reaction step in a multi-step mechanism whose stoichiometric coefficients match the reaction order exponents in its rate law.

Molecularity

The number of reactant particles that come together to collide in an individual elementary step (classified as unimolecular, bimolecular, or termolecular).

Reaction Intermediate

A chemical species produced in an early elementary step of a mechanism and consumed in a later elementary step, meaning it does not appear in the overall balanced equation.

Transition State

An unstable, high-energy arrangement of atoms at the maximum point of an energy profile where old bonds are breaking and new bonds are forming.

Rate-Limiting Step

The slowest elementary reaction in a multistep mechanism that governs and limits the overall rate of the chemical reaction.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed by offering an alternative pathway with a lower activation energy ($E_a$).

Lock-and-Key Model

An enzyme catalysis model postulating that the substrate has a shape complementary to the enzyme's active site and fits rigidly without conformational changes.

Induced Fit Model

A model of enzyme catalysis where the active site undergoes conformational changes upon substrate binding to optimize active catalytic interactions.

Enantiomers

Non-superimposable mirror-image stereoisomers that share most identical physical properties but rotate plane-polarized light in opposite directions and interact differently with chiral environments.

Chiral Center

An atom (most commonly a carbon atom) bonded to four distinct chemical substituents, rendering the molecule chiral and lacking an internal plane of symmetry.

Racemization

The process by which an optically active, pure enantiomeric sample (such as $\text{L}$-alanine) equilibrates over time into an equal mixture of both $\text{L}$ and $\text{D}$ isomers.

Second Law of Thermodynamics

The fundamental law stating that for any thermodynamically favored (spontaneous) process in an isolated system, the total entropy increases: $\Delta S_{\text{TOTAL}} = \Delta S_{\text{sys}} + \Delta S_{\text{surr}} > 0$.

Gibbs Free Energy ($\Delta G_{\text{rxn}}$)

A thermodynamic potential defined as $\Delta G_{\text{rxn}} = \Delta H_{\text{rxn}} - T\Delta S_{\text{rxn}}$; a negative value ($\Delta G < 0$) indicates that a process is product-favored at constant temperature and pressure.

Thermodynamic Reaction Directionality Rules

The four criteria governing reaction spontaneity based on enthalpy and entropy: $\Delta H < 0, \Delta S > 0$ (always product-favored); $\Delta H > 0, \Delta S < 0$ (always reactant-favored); and matching signs where directionality depends on temperature.

Standard Enthalpy of Formation ($\Delta H_f^\circ$)

The enthalpy change when one mole of a substance is formed from its constituent elements in their standard states at $25\,^{\circ}\text{C}$ and $1\,\text{atm}$, defined as zero for pure elementary substances.

Standard Molar Entropy ($S^\circ$)

The absolute entropy of one mole of a pure substance in its standard state at $25\,^{\circ}\text{C}$ and $1\,\text{atm}$, having a positive value for all substances.

Chemical Equilibrium

A dynamic state reached when the rates of the forward and reverse chemical reactions are equal, causing the concentrations or partial pressures of all reactants and products to remain constant.

Equilibrium Constant ($K$)

A temperature-dependent ratio of equilibrium concentrations or partial pressures of products raised to their stoichiometric coefficients over those of reactants; related to free energy by $\Delta G^\circ = -RT \ln(K)$.

Product-Favored Process

A chemical reaction that proceeds until products dominate reactants at equilibrium, characterized by $\Delta G^\circ < 0$ and an equilibrium constant $K > 1$.

Reactant-Favored Process

A chemical reaction that establishes equilibrium while mostly remaining as reactants, characterized by $\Delta G^\circ > 0$ and an equilibrium constant $K < 1$.