Gen Chem Key Terms Ch. 16 (after Rate Law) to Ch. 19 (including Acid-Base Titrations)

activation energy (Ea)

The minimum energy with which molecules must collide to react.

catalyst

A substance or mixture that increases the rate of a reaction without being used up in the process.

Arrhenius equation

An equation that expresses the exponential relationship between temperature and the rate constant

average rate

The change in concentration of reactants (or products) divided by a finite time period.

bimolecular reaction

An elementary reaction involving the collision of two reactant species.

chemical kinetics

The study of the rates of reactions and the factors that affect them.

effective collision

A collision in which the particles meet with sufficient energy and an orientation that allows them to react.

collision theory

A model that explains reaction rate as based on the number, energy, and orientation of colliding particles.

elementary reaction

(also elementary step) A simple reaction that describes a single molecular event in a proposed reaction mechanism.

enzyme

A biological macromolecule (usually a protein) that acts as a catalyst.

enzyme-substrate complex (ES)

The intermediate in an enzyme-catalyzed reaction, which consists of enzyme and substrate(s) and whose concentration determines the rate of product formation.

frequency factor (A)

The product of the collision frequency Z and an orientation probability factor p that is specific for a reaction.

half-life (t1/2)

In chemical processes, the time required for the reactant concentration to reach half of its initial value. In nuclear processes, the time required for half the initial number of nuclei in a sample to decay.

heterogeneous catalyst

A catalyst that occurs in a different phase from the reactants, usually a solid interacting with gaseous or liquid reactants.

homogeneous catalyst

A catalyst (gas, liquid, or soluble solid) that exists in the same phase as the reactants.

hydrogenation

The addition of hydrogen to a carbon-carbon multiple bond to form a carbon-carbon single bond.

induced-fit model

A model of enzyme action that pictures the binding of the substrate as inducing the active site to change its shape and become catalytically active.

instantaneous rate

The reaction rate at a particular time, given by the slope of a tangent to a plot of reactant concentration vs. time.

integrated rate law

A mathematical expression for reactant concentration as a function of time.

lock-and-key model

A model of enzyme function that pictures the enzyme active site and the substrate as rigid shapes that fit together as a lock and key, respectively.

molecularity

The number of reactant particles involved in an elementary step.

rate-determining step

(also rate-limiting step) The slowest step in a reaction mechanism and therefore the step that limits the overall rate.

rate law

(also rate equation) An equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature.

reaction energy diagram

A graph that shows the potential energy of a reacting system as it progresses from reactants to products.

reaction intermediate

A substance that is formed and used up during the overall reaction and therefore does not appear in the overall equation.

reaction mechanism

A series of elementary steps that sum to the overall reaction and is consistent with the rate law.

reaction order

The exponent of a reactant concentration in a rate law that shows how the rate is affected by changes in that concentration.

substrate

A reactant that binds to the active site in an enzyme-catalyzed reaction.

transition state theory

A model that explains how the energy of reactant collisions is used to form a high-energy transitional species that can change to reactant or product.

transition state

The state of an unstable species formed in an effective collision of reactants that exists momentarily when the system is highest in energy and that can either form products or re-form reactants.

activated complex

The unstable species formed in an effective collision of reactants that exists momentarily when the system is highest in energy and that can either form products or re-form reactants.

unimolecular reaction

An elementary reaction that involves the decomposition or rearrangement of a single particle.

equilibrium constant (K)

The value obtained when equilibrium concentrations are substituted into the reaction quotient.

Haber process

An industrial process used to form ammonia from its elements.

law of chemical equilibrium

(also law of mass action) The law stating that, when a system reaches equilibrium at a given temperature, the ratio of quantities that make up the reaction quotient has a constant numerical value.

Le Châtelier’s principle

A principle stating that, if a system in a state of equilibrium is disturbed, it will undergo a change that shifts its equilibrium position in a direction that reduces the effect of the disturbance.

reaction quotient (Q)

(also mass-action expression) A ratio of terms for a given reaction consisting of product concentrations multiplied together and divided by reactant concentrations multiplied together, with each concentration raised to the power of its balancing coefficient. The value of Q changes until the system reaches equilibrium, at which point it equals K.

van’t Hoff equation

An equation for calculating the change in equilibrium constant that occurs with a change in temperature

acid-base indicator

An organic molecule whose color is different in acid and in base; the color is used to monitor the equivalence point of a titration or the pH of a solution.

acid-dissociation (acid-ionization) constant (Ka)

An equilibrium constant for the dissociation of an acid (HA) in H2O to yield the conjugate base (A−) and H3O+

adduct

The product of a Lewis acid-base reaction, a species that contains a new covalent bond.

amphiprotic

A substance that can either donate or accept a proton (H+).

Arrhenius Acid

a substance that yields hydrogen ions

Arrhenius Base

a substance that yields hydroxide ions

autoionization

(also self-ionization) A reaction in which two molecules of a substance react to give ions. The most important example is for water

base-dissociation (base-ionization) constant (Kb)

An equilibrium constant for the reaction of a base (B) with H2O to yield the conjugate acid (BH+ and OH−

Brønsted-Lowry acid

a proton donor

Brønsted-Lowry base

a proton acceptor

conjugate acid-base pair

Two species related to each other through the gain or loss of a proton; the acid has one more proton than its conjugate base.

hydronium ion (H3O+)

A proton covalently bonded to a water molecule.

ion-product constant for water (Kw)

The equilibrium constant for the autoionization of water; equal to 1.0 × 10−14 at 298 K.

leveling effect

The inability of a solvent to distinguish the strength of an acid (or base) that is stronger than the conjugate acid (or conjugate base) of the solvent.

Lewis Acid

electron pair acceptor

Lewis Base

electron pair donor

neutralization

The process that occurs when an H+ ion from an acid combines with an OH− ion from a base to form H2O.

pH

The negative of the common logarithm of [H3O+].

polyprotic acid

An acid with more than one ionizable proton.

common-ion effect

The shift in the position of an ionic equilibrium away from an ion involved in the process that is caused by the addition or presence of that ion.

complex ion

An ion consisting of a central metal ion covalently bonded to two or more anions or molecules, called ligands.

end point

The point in a titration at which the indicator changes color permanently.

equivalence point

The point in a titration when the number of moles of the added species is stoichiometrically equivalent to the original number of moles of the other species.

ligand

A molecule or an anion bonded to a central metal ion in a complex ion.